User interface language: English | Español

Date May 2019 Marks available 7 Reference code 19M.2.AHL.TZ2.H_7
Level Additional Higher Level Paper Paper 2 Time zone Time zone 2
Command term Prove Question number H_7 Adapted from N/A

Question

Suppose that u 1 is the first term of a geometric series with common ratio r .

Prove, by mathematical induction, that the sum of the first n terms, s n is given by

s n = u 1 ( 1 r n ) 1 r , where n Z + .

Markscheme

* This question is from an exam for a previous syllabus, and may contain minor differences in marking or structure.

n = 1 s 1 = u 1 , so true for  n = 1               R1

assume true for  n = k , ie.  s k = u 1 ( 1 r k ) 1 r               M1

Note: Award M0 for statements such as “let n = k ”.

Note: Subsequent marks after the first M1 are independent of this mark and can be awarded.

s k + 1 = s k + u 1 r k               M1

s k + 1 = u 1 ( 1 r k ) 1 r + u 1 r k          A1

s k + 1 = u 1 ( 1 r k ) 1 r + u 1 r k ( 1 r ) 1 r

s k + 1 = u 1 u 1 r k + u 1 r k r u 1 r k 1 r          A1

s k + 1 = u 1 ( 1 r k + 1 ) 1 r          A1

true for n = 1 and if true for n = k then true for n = k + 1 , the statement is true for any positive integer (or equivalent).        R1

Note: Award the final R1 mark provided at least four of the previous marks are gained.

[7 marks]

Examiners report

[N/A]

Syllabus sections

Topic 1—Number and algebra » SL 1.2—Arithmetic sequences and series
Show 111 related questions
Topic 1—Number and algebra

View options