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1.2 Numbers and Algebra

Q1

Topic
1.2 Numbers and Algebra
Tag
Sequences; Series; Arithmetic; Geometric; Sigma; Compound interest; Finance
Source
M17/5/MATHL/HP1/ENG/TZ1/XX/7
Question Text
An arithmetic sequence u1,u2,u3u₁, u₂, u₃ has u1=2u₁ = -2 and common difference d0d ≠ 0. (a) Given that u3,u4u₃, u₄ and u6u₆ are the first three terms of a geometric sequence, find the value of dd;
Total Mark
4
Correct Answer
2
Explanation
n/a
Mark Scheme
Step 1: Consider the given information Given information are u1=2u₁= -2, and that u3,u4u₃, u₄ and u6u₆ form a geometric sequence. Step 2: Combine the given information u3=u1+2d,u4=u1+3d,u6=u1+5du₃ =u₁ + 2d, u₄ = u₁+3d, u₆ = u₁ + 5d Step 3: We haven’t used the geometric sequence yet so, u3,u4,u6=a,ar,ar2u₃, u₄, u₆ = a, ar, ar² We can notice that, (ar)2=a×ar2u42=u3×u6(ar)²=a \times ar²\\ u₄²=u₃\times u₆ Replacing the current variables what we determined in step 2, (2+3d)2=(2+2d)(2+5d)(-2+3d)² = (-2+2d)(-2+5d) Expand and simplify d22d=d(d2)=0d=0 or 2d²-2d = d(d-2)=0\\ d=0~or~2 So, d=2d=2
Question Text
(b) Given that un=18uₙ=18, where n is a positive integer, determine the value of r=1nur\sum_{r=1}^{n}u_{r}.
Total Mark
3
Correct Answer
88
Explanation
n/a
Mark Scheme
Step 1: Point out the given information, d=2d = 2 from part (a), un=18u_{n}=18 and u1=2u_{1}=-2 Step 2: Combine the given information to find useful information un=u1+(n1)du_{n} =u_1+(n-1)d 18=2+(n1)×2,18 = -2 + (n - 1) \times 2, so n=11n = 11 Step 3: Refer back to the question: determine the value of r=1nur\sum_{r=1}^{n}u_{r} r=111ur=sum\sum_{r=1}^{11}u_{r}=sum of the first 11 terms of the arithemtic sequence, given by the formula, n(u1+un)2\frac{n(u_{1}+u_{n})}{2} r=111ur=11(182)2=88\sum_{r=1}^{11}u_{r}=\frac{11(18-2)}{2}=88 Answer: 88

Q2

Topic
1.2 Numbers and Algebra
Tag
Sequences; Series; Arithmetic; Geometric; Sigma; Compound interest; Finance
Source
M17/5/MATHL/HP1/ENG/TZ2/XX/3
Question Text
The 1st, 3rd, and 6th terms of an arithmetic sequence, with common difference d,d0d, d≠0, are the first three terms of a geometric sequence, with common ratio r. Given that the 1st term of both sequences is 4. (a) Find the value of dd.
Total Mark
4
Correct Answer
1
Explanation
n/a
Mark Scheme
Step 1: Consider the given information. Given information are u1=4u_{1}=4 and r1=4r_{1}=4 and that u1,u3u_{1}, u_3 and u6u_{6} from a geometric sequence. Step 2: Combine the given information. u1=4,u3=4+2d,u6=4=5du_{1}=4, u_3=4+2d, u_6=4=5d If we use the information that the 1st, 3rd, and 6th terms of the arithmetic sequence form a geometric sequence, u1×d=u3u3×d=u6u_{1}\times d=u_{3}\\ u_{3} \times d=u_{6} Then, we can attempt to find the value of dd. 4+2d4=4+5d4+2d \frac{4+2d}{4} = \frac{4+5d}{4+2d} Expand and simplify. (4+2d)(4+2d)=4(4+5d)d=1 or 0(4+2d)(4+2d) = 4(4+5d)\\ d = 1~or~0 Since d0,d=1d\neq 0, d=1 Answer = 1
Question Text
(b) Find the value of 2r 2r.
Total Mark
1
Correct Answer
3
Explanation
n/a
Mark Scheme
Step 1: Point out the given information, d=1frompart(a)anda=4.d=1 from part (a) and a=4. Step 2: Combine the given information. Use the value of d to find the first two terms of the geometric sequence. a=u1=4ar=u3=4+2(1)=6a = u₁= 4\\ ar = u₃= 4 + 2(1) = 6 Hence, we can find rr by using ratios. r=ara=64=32r=\mathrm{\frac{ar}{a}}=\frac{6}{4}=\frac{3}{2} Hence, 2r=32r = 3

Q3

Topic
1.2 Numbers and Algebra
Tag
Sequences; Series; Arithmetic; Geometric; Sigma; Compound interest; Finance
Source
N16-TZ0-P1-6(HL)
Question Text
The sum of the first n terms of a sequence {un}\left\{u_{n} \right\} is given by Sn=4n25nSₙ=4n²-5n, where nZ+n∈Z^+. (a) Write down the value of u1u₁.
Total Mark
1
Correct Answer
1
Explanation
n/a
Mark Scheme
u1=1u₁= 1
Question Text
(b) Find the value of u7u₇.
Total Mark
2
Correct Answer
47
Explanation
n/a
Mark Scheme
u7=S7S6=4(72)5(7)4(62)+5(6)=47u₇= S₇- S₆= 4(72) - 5(7) - 4(62) + 5(6) = 47 Answer: 47
Question Text
(c) Given that {uₙ} is an arithmetic sequence, clearly state its common difference.
Total Mark
4
Correct Answer
8
Explanation
n/a
Mark Scheme
Step 1: Consider the given information and identify what we need to prove. If we assume un to be an arithmetic sequence, we can find the expression for the arithmetic sequence by using the following expression. un=SnSn1uₙ= Sₙ - Sₙ₋₁ Step 2: Combine the given information. Substitute the sum of the arithmetic sequence expression into SnSₙ and Sn1Sₙ₋₁. un=(4n25n)(4(n1)25(n1))=(4n25n)(4n28n+45n+5)=8n+1uₙ = (4n²-5n) - (4(n-1)²-5(n-1)) = (4n²-5n) - (4n²-8n+4-5n+5) = 8n+1 Now, we can find the common difference using the arithmetic sequence. d=un+1un=8(n+1)+1(8n+1)=8(constant)d = uₙ₊₁ - uₙ = 8(n+1)+1-(8n+1) = 8(constant)

Q4

Topic
1.2 Numbers and Algebra
Tag
Sequences; Series; Arithmetic; Geometric; Sigma; Compound interest; Finance
Source
M16-TZ1-P1-1(HL)
Question Text
The seventh term of an arithmetic sequence is equal to 3 and the sum of the first 16 terms is 24. (a) Find the common difference.
Total Mark
3
Correct Answer
-1
Explanation
n/a
Mark Scheme
Step 1: Consider the given information. We know that the 7th term of the arithmetic sequence is 3 and the sum of the first 16 terms is 24. u7=u1+6d=3S16=(16/2)(2u1+(161)d)=8(2u1+15d)=24u₇ = u₁+ 6d = 3 S₁₆= (16/2)(2u₁+(16-1)d) = 8(2u₁+15d) = 24 Step 2: Combine the given information. We can combine the two equations by expressing u₁ in terms of dd. u1=36dS16=8(2(36d)+15d)=24d=1u₁ = 3 - 6d S₁₆ = 8(2(3-6d) + 15d) = 24 d = -1 Answer: -1
Question Text
(b) Find the first term.
Total Mark
3
Correct Answer
9
Explanation
n/a
Mark Scheme
Now, we can use the value of dd to find the first term. u1=36(1)=9u₁ = 3 - 6(-1) = 9 Answer: 9

Q5

Topic
1.2 Numbers and Algebra
Tag
Sequences; Series; Arithmetic; Geometric; Sigma; Compound interest; Finance
Source
M15-TZ1-P1-12(HL)
Question Text
Let {un},nZ+\left\{u_{n} \right\},n\in Z^{+}, be an arithmetic sequence with first term equal to α \alpha and common difference of dd, where d0d\neq 0. Let another sequence {vn},nZ+\left\{v_{n} \right\},n\in Z^{+}, be defined by vn=3un+2nv_{n}=3^{u_{n}+2_{n}}. (a) (i) Given that vn+1vn\frac{v_{n+1}}{v_{n}} is a constant and can be expressed in terms 3d+k3^{d+k}, find the value of kk. Total Mark: 2 Correct Answer: 2 Explanation: n/a Mark Scheme: vn+1vn=3un+1+2(n+1)3un+2n=3un+1+2n+2un2n=3d+2\frac{v_{n+1}}{v_{n}}=\frac{3^{u_{n+1}+2(n+1)}}{3^{u_{n}+2n}}=3^{u_{n+1}+2n+2-u_{n}-2n}=3^{d+2} (ii) Write down the first term of the sequence {vn}\left\{ v_{n}\right\}. (a) 3a3^{a} (b) 3a+23^{a+2} (c) 32a 3^{2a} (d) 32a+23^{2a+2} Total Mark: 1 Correct Answer: (b) Explanation: n/a Mark Scheme: x (iii) Write down a formula for vnvₙ in terms of a, d and n. (a) 3ad+2n3^{ad+2n} (b) 3a+(n1)d+n3^{a+(n-1)d+n} (c) 3a+nd+2n 3^{a+nd+2n} (d) 3a+(n1)d+2n3^{a+(n-1)d+2n} Total Mark: 1 Correct Answer: (d) Explanation: n/a Mark Scheme: x
Question Text
(b) Let {Sₙ} be the sum of the first n terms of the sequence {vₙ}. (i) Find {Sₙ}, in terms of a, d and n. (a) 3a+3((3d+3)n1)3d+31\frac{3^{a+3}\left ( (3^{d+3})^{n}-1 \right )}{3^{d+3}-1} (b) 3a+2((3d+2)n1)3d+21\frac{3^{a+2}\left ( (3^{d+2})^{n}-1 \right )}{3^{d+2}-1} (c) 3a+2((3d+1)n1)3d+21\frac{3^{a+2}\left ( (3^{d+1})^{n}-1 \right )}{3^{d+2}-1} (d)3a+2((3d+2)n1)3d+21 \frac{3^{a+2}\left ( (3^{d+2})^{n}-1 \right )}{3^{d+2}-1} Total Mark: 1 Correct Answer: (d) Explanation: n/a Mark Scheme: x (ii) Find range of d for which i=1vi\sum_{i=1}^{\infty} v_{i} exists. (a) d>2d>2 (b) d<2d<2 (c) d<2d<-2 (d) d<2d<-2 Total Mark: 3 Correct Answer: (c) Explanation: n/a Mark Scheme: For the sum of infinity to exist, the following condition must be satisfied. 1<3d+2<1-1<3^{d+2}<1 19<3d<19-\frac{1}{9}<3^{d}<\frac{1}{9} 3d<323^{d}<3^{-2} d<2d<-2 (iii) You are now told that i=1vi \sum_{i=1}^{\infty }v_{i} does exist and is denoted by SS_{\infty }. (a) 3a+23d+21\frac{3^{a+2}}{3^{d+2}-1} (b) 3d+213a+2\frac{3^{d+2}}{1-3^{a+2}} (c) 3a+23d+2\frac{3^{a+2}}{3^{d+2}} (d) 3a+213d+2 \frac{3^{a+2}}{1-3^{d+2}} Total Mark: 1 Correct Answer: (d) Explanation: n/a Mark Scheme: Substitute u₁ and r into S∞ equation, as |r| is given to be less than 1. (iv) Given that S=272(3a)S_{\infty } =\frac{27}{2}(3^{a}) find the value of dd. Total Mark: 3 Correct Answer: -3 Explanation: n/a Mark Scheme: Utilize your answer from (iii) and substitute it into the equation. 3a+213d+2=272(3a)\frac{3^{a+2}}{1-3^{d+2}}=\frac{27}{2}(3^{a}) 3213d+2=272\frac{3^{2}}{1-3^{d+2}}=\frac{27}{2} 113d+2=32\frac{1}{1-3^{d+2}}=\frac{3}{2} 33d+3=23-3^{d+3}=2 d=3d=-3

Q6

Topic
1.2 Numbers and Algebra
Tag
Sequences; Series; Arithmetic; Geometric; Sigma; Compound interest; Finance
Source
M15-TZ1-P1-12(HL)
Question Text
Let wn,nZ+wₙ, n\in Z^{+}, be a geometric sequence with first term equal to p and common ratio qq, where pp and qq are both greater than zero. Let another sequence znzₙ be defined by zn=log(wn)zₙ = log⁡(wₙ). Find ι=1nzι\sum_{\iota =1}^{n}z_{\iota }, giving your answer in the form InkInk with kk in terms of n,pn, p and qq. (a) log(pnqn)log(p^n{q^{n}}) (b) log(pnq(n1)2)log(p^n{q^{\frac{(n-1)}{2}}}) (c) log(pnqn2)log(p^n{q^{\frac{n}{2}}}) (d) log(pnqn(n1)2)log(p^n{q^{\frac{n(n-1)}{2}}})
Total Mark
6
Correct Answer
(d)
Explanation
n/a
Mark Scheme
We can express znz_{n} in terms of pp and qq. wn=pqn1w_{n}=pq^{n-1} zn=logpqn1z_{n}=logpq^{n-1} zn=logp+(n1)logqz_{n}=logp+(n-1)logq Using this expression, we can find the first term and common difference of the {znz_{n}} sequence. zn+1zn=(logp+nlogq)(logp+(n1)logq)=logqz_{n+1}-z_{n}=(logp+nlogq)-(logp+(n-1)logq)=logq Hence, {znz_{n}} is an arithmetic sequence with the first term being logplogp and the common difference being logq logq Finally, we can find the sum of the arithmetic sequence as below. i=1nzi=n2(2logp+(n1)logq)=n(logp+logq(n12))=nlog(pq(n12))=log(pnqn(n1)2) \sum_{i=1}^{n}z_{i}=\frac{n}{2}(2logp+(n-1)logq)=n\left ( logp+logq^{\left ( \frac{n-1}{2} \right )} \right )=nlog\left ( pq^{\left ( \frac{n-1}{2} \right )} \right )=log\left ( p^{n}q^{\frac{n(n-1)}{2}} \right ) or i=1nzi=logp+logpq+logpq2+...+logpqn1=log(pnq(1+2+3+...+(n1)))=log(pnqn(n1)2)\sum_{i=1}^{n}z_{i}=logp+logpq+logpq^{2}+...+logpq^{n-1}=log\left ( p^{n}q^{(1+2+3+...+(n-1))} \right )=log\left ( p^{n}q^{\frac{n(n-1)}{2}} \right ) Answer: (d)

Q7

Topic
1.2 Numbers and Algebra
Tag
Sequences; Series; Arithmetic; Geometric; Sigma; Compound interest; Finance
Source
M14/5/MATHL/HP1/ENG/TZ1/X/13
Question Text
A geometric sequence unuₙ, with complex terms, is defined by un+1=(1i)un and u1=4uₙ₊₁ = (1 - i)uₙ ~and~ u₁=4. (a) Find the fourth term of the sequence, giving your answer in the form x+yi,(x,yR)x + yi , (x,y ∈ R).
Total Mark
2
Correct Answer
88i-8-8i
Explanation
n/a
Mark Scheme
METHOD 1 Solve the fourth term by following through the sequence. u1=4u2=44iu3=8iu4=88u₁ = 4\\ u₂ = 4 - 4i\\ u₃ = - 8i\\ u₄ = - 8 - 8ii METHOD 2 Calculate the fourth term by understanding the pattern. u4=4(1i)3=88iu₄ = 4(1 - i)³ = - 8 - 8i Answer: 88i-8-8i
Question Text
(b) Find the sum of the first 20 terms of {un}\left\{ u_{n }\right\}. Giving your answer in the form a×(1+2m)a×(1+2ᵐ), find the sum of aa and mm.
Total Mark
3
Correct Answer
14
Explanation
n/a
Mark Scheme
Use the summation formula for geometric sequences (formula booklet) S20=4((1i)201)iS_{20}=\frac{4((1-i)^{20}-1)}{i} =4((2i)101)i=\frac{4((-2i)^{10}-1)}{i} =4(2101)i=\frac{4(2^{10}-1)}{i} =4(210+1)=4(2^{10}+1) Answer: 14
Question Text
(c) Given that vnv_n is a geometric sequence, its first term can be expressed as p(1i)k((1i)2)n1.p(1 - i)ᵏ((1 - i)²)ⁿ⁻¹. Find the value of nn.
Total Mark
2
Correct Answer
16
Explanation
n/a
Mark Scheme
Rearrange the expression for vnvₙ to find the general formula of the geometric sequence. vn=(4(1i)n1(4(1i)n1+k)=16(1i)k(1i)2n2=16(1i)k(1i)2n1(=16(1i)k(2i)n1)vₙ = (4(1 - i)ⁿ⁻¹(4(1-i)ⁿ⁻¹⁺ᵏ)\\ = 16(1-i)ᵏ(1-i)²ⁿ⁻²\\ = 16(1 - i)ᵏ(1 - i)²ⁿ⁻¹(=16(1 - i)ᵏ(-2i)ⁿ⁻¹) Hence, the value of p is 16. Answer: 16
Question Text
A third sequence wnw_n is defined by wn=unun+1wₙ = | uₙ - uₙ₊₁ |. (d) Given that wnwₙ forms a geometric sequence with a common ratio of √k, state the value of kk. (a) 2(2)n2(\sqrt{2})^{n} (b) 2(2)n+12(\sqrt{2})^{n+1} (c) 4(2)n4(\sqrt{2})^{n} (d) 4(2)n+14(\sqrt{2})^{n+1}
Total Mark
4
Correct Answer
(d)
Explanation
n/a
Mark Scheme
Find the general formula of the geometric sequence. wn=4(1i)n14(1i)n=41in111i=41in1=4(2)n1wₙ = |4(1 - i)ⁿ⁻¹-4(1 - i)ⁿ|\\ = 4|1 - i|ⁿ⁻¹|1 - 1 - i|\\ = 4|1 - i|ⁿ⁻¹\\ = 4(√2)ⁿ⁻¹ Answer: (d)

Q8

Topic
1.2 Numbers and Algebra
Tag
Sequences; Series; Arithmetic; Geometric; Sigma; Compound interest; Finance
Source
M14/5/MATHL/HP1/ENG/TZ2/XX/9
Question Text
The first three terms of a geometric sequence are cosx,sin2xcosx, sin2x, and (π2<x<π2)(-\frac{\pi }{2}<x<\frac{\pi }{2}) (a) Find the common ratio rr.
Total Mark
2
Correct Answer
2sin(x)2sin(x)
Explanation
n/a
Mark Scheme
To find the common ratio of the geometric sequence, we can divide the second term by the first term. r=sin(2x)cos(x)=2sin(x)cos(x))cos(x)=2sin(x)r=\frac{sin(2x)}{cos(x)}=\frac{2sin(x)cos(x))}{cos(x)}=2sin(x)
Question Text
(b) Find the set of values of x for which the geometric series sinx+sin2x+2sin2xcosx+sinx +sin2x +2 sin²x cosx+… converges. (a) π2<x<π6 or π6<x<π2-\frac{\pi}{2}<x<-\frac{\pi }{6} ~or~ \frac{\pi }{6}<x<\frac{\pi }{2} (b) π2<x<π4 or π4<x<π2-\frac{\pi}{2}<x<-\frac{\pi }{4} ~or~ \frac{\pi }{4}<x<\frac{\pi }{2} (c) π4<x<π6 or π6<x<π4-\frac{\pi}{4}<x<-\frac{\pi }{6} ~or~ \frac{\pi }{6}<x<\frac{\pi }{4} (d) π3<x<π6 or π6<x<π3-\frac{\pi}{3}<x<-\frac{\pi }{6} ~or~ \frac{\pi }{6}<x<\frac{\pi }{3}
Total Mark
4
Correct Answer
(a)
Explanation
n/a
Mark Scheme
For the geometric series to converge, the absolute value of the common ratio should be smaller than 1.|r|<1 r<12sin x<1|r|<1 \\|2sin~x|<1 or 1<r<11<2sin x<1-1 < r < 1 \\-1 < 2sin~x <1 then 0<sinx<12 forπ6<x<π6π2<x<π6orπ6<x<π20<sinx<\frac{1}{2}~for-\frac{\pi }{6}<x<\frac{\pi }{6}\\ -\frac{\pi }{2} <x<-\frac{\pi }{6}or\frac{\pi }{6}<x<\frac{\pi }{2} Answer: (a)
Question Text
(c) Given that the sum to infinity of this series is 12(t15)\frac{1}{2(t-\sqrt{15})}, find the value of tt.
Total Mark
4
Correct Answer
2
Explanation
n/a
Mark Scheme
Use the sum of infinite geometric series formula to find the value of tt S=cosx12sinx=cos(arcos(14))12sin(arccos(14))=141152=12(215)S_{\infty }=\frac{cosx}{1-2sinx}=\frac{cos(arcos(\frac{1}{4}))}{1-2sin(arccos(\frac{1}{4}))}=\frac{\frac{1}{4}}{1-\frac{\sqrt{15}}{2}}=\frac{1}{2(2-\sqrt{15})} Hence, the value of tt is equal to 2. Answer: 2

Q9

Topic
1.2 Numbers and Algebra
Tag
Sequences; Series; Arithmetic; Geometric; Sigma; Compound interest; Finance
Source
N13-TZ0-P1-7(HL)
Question Text
The sum of the first two terms of a geometric series is 20 and the sum of the first four terms is 40. (a) Find the value of r2.
Total Mark
4
Correct Answer
4
Explanation
n/a
Mark Scheme
Step 1: Consider the given information. The question has provided us the sum of the first two terms and sum of the first tour terms. We can express the given information as an equation. a+ar=10a+ar+ar2+ar3=50a+ar=10\\a+ar+ar^2+ar^3=50 Stop 2: Combine the given information. We can combine the two equation to find the value of r2r^2. ar2+ar3=40r2(a+ar)=40r2=4ar^2+ar^3=40 \\r^2(a+ar)=40\\ r^2=4 Answer: 4
Question Text
(b) Given r=2,r=2, (i) the first term will be in the form x3\frac {x}{3}. Find xx. Total Mark: 1 Correct Answer: 10 Explanation: n/a Mark Scheme: To find the first term, we need to find the value of a using the given rr value. a+2a=10a=103x=10a+2a=10 \\a=\frac{10}{3} \\x=10 Answer: 10 (ii) find the sum of the first ten terms. Total Mark: 2 Correct Answer: 3410 Explanation: n/a Mark Scheme: We can use the sum of geometric series to find the value of S10S_{10}. S10=103(210121)=3410S_{10}=\frac{10}{3}\left ( \frac{2^{10}-1}{2-1} \right )=3410 Answer: 3410

Q10

Topic
1.2 Numbers and Algebra
Tag
Sequences; Series; Arithmetic; Geometric; Sigma; Compound interest; Finance
Source
M13-TZ1-P1-8(HL)
Question Text
The first terms of an arithmetic sequence are 1log3x,1log27x,1log243x,1log2187x,\frac{1}{log_{3}x},\frac{1}{log_{27}x},\frac{1}{log_{243}x},\frac{1}{log_{2187}x},… Find xx if the sum of the 20 terms of the sequence is equal to 100.
Total Mark
6
Correct Answer
27
Explanation
n/a
Mark Scheme
Tip 1: Find the common difference of the arithmetic sequence. d=1log27x1log3x=log327log3xlog33log3x=2log3xd=\frac{1}{log_{27}x}-\frac{1}{log_{3}x}=\frac{log_{3}27}{log_{3}x}-\frac{log_{3}3}{log_{3}x}=\frac{2}{log_{3}x} Tip 2: Find the value of xx by using the given information that the sum of the first 12 terms is equal to 48. The sum of the first 12 terms in the arithmetic sequence can be found by using the following formula. S12=122(2×1log3x+11×2log3x)=48144log3x=48log3x=3S_{12}=\frac{12}{2}(2\times \frac{1}{log_{3}x}+11\times \frac{2}{log_{3}x})=48\\ \frac{144}{log_{3}x} =48 \\log_{3}x=3 Hence, we can find xx. x=33=27x=3^3=27 Answer: 27

Q11

Topic
1.2 Numbers and Algebra
Tag
Sequences; Series; Arithmetic; Geometric; Sigma; Compound interest; Finance
Source
M13-TZ2-P1-6(HL)
Question Text
A geometric sequence has first term aa, common ratio r and sum to infinity 36. A second geometric sequence has first term aa, common ratio r3 and sum to infinity 16. Given that the value of rr can be expressed as r=x12r=\frac{\sqrt{x}-1}{2} find the value of xx.
Total Mark
7
Correct Answer
26
Explanation
n/a
Mark Scheme
Step 1: Consider the given information. We can express the first series as a1r=36\frac{a}{1-r}=36 and the second series as a1r3=16 \frac{a}{1-r^{3}}=16 Step 2: Combine the given information. To solve for the value of rr, we can attempt eliminate aa by using the substitution method. 36(1r)1r3=16\frac{36(1-r)}{1-r^{3}}=16 Simplify and obtain 4r2+4r5=0r=1±624r^{2}+4r-5=0 \\r=\frac{-1\pm \sqrt{6}}{2} Hence, the value of rr is equal to r=612r=\frac{\sqrt{6}-1}{2}. Answer: 6

Q12

Topic
1.2 Numbers and Algebra
Tag
Sequences; Series; Arithmetic; Geometric; Sigma; Compound interest; Finance
Source
M19/5/MATHL/HP1/ENG/TZ2/XX/1
Question Text
In an arithmetic sequence, the sum of the 4th and 6th term is -2. Given that the sum of the first eight terms is 8, determine the sum of the first term and the common difference.
Total Mark
1
Correct Answer
11
Explanation
n/a
Mark Scheme
Attempt to from two equation involving the first term and the common difference to find their values. (1) (u1+3d)+(u1+5d)=22u1+8d=2\left( u_{1}+3d \right )+(u_{1}+5d)=-2\\ 2u_{1}+8d=-2 (2) 82[2u1+7d]=82u1+7d=2\frac{8}{2}\left [ 2u_{1}+7d \right ]=8\\ 2u_{1} +7d=2 Hence, the first term and common difference can be determined as the following u1=15,d=4u_{1}=15, d=-4 The sum of the two terms is equal to 11. Answer: 11

Q13

Topic
1.2 Numbers and Algebra
Tag
Sequences; Series; Arithmetic; Geometric; Sigma; Compound interest; Finance
Source
M18/5/MATHL/HP1/ENG/TZ2/XX/5
Question Text
The geometric sequence u1,u2,u3,u₁, u₂, u₃,… has a common ratio rr. Consider the sequence A={an=log3un:nZ+}A=\left\{a_{n}=log_{3}|u_{n}|:n\in Z^{+} \right\} (a) Given that AA is an arithmetic sequence, state its common difference dd in terms of rr. (a) log3rlog_3|r| (b) log3r+1log_3|r+1| (c) log33rlog_3|3r| (d) log3r2log_3|r^2|
Total Mark
4
Correct Answer
(a)
Explanation
n/a
Mark Scheme
Tip 1: Find an expression for the common difference dd. Using the given information, the arithmetic sequence’s common difference can be expressed as d=an+1an=log3un+1log3un=log3un+1und=a_{n+1} -a_{n}\\ =log_{3}\left| u_{n+1}\right|-log_{3}\left|u_{n} \right|\\ =log_{3}\left| \frac{u_{n+1}}{u_{n}}\right| Tip 2: Use the information that u1,u2,u3u_1, u_2, u_3 is a geometric sequence. Since we know that unu_n is a geometric sequence, we can express the common difference in terms of rr. d=log3rd=log_{3}|r|
Question Text
(b) Find the value of dd.
Total Mark
3
Correct Answer
-1
Explanation
n/a
Mark Scheme
We are given the information that the sum to infinity of the geometric sequence is equal to 4. 81r=9r=13d=log313=1\frac{8}{1-r}=9\\ r=\frac{1}{3}\\ d=log_{3}|\frac{1}{3}|=-1 Answer: -1 ..................................................................\underline{..................................................................}