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Date May 2017 Marks available 9 Reference code 17M.1.AHL.TZ2.H_8
Level Additional Higher Level Paper Paper 1 (without calculator) Time zone Time zone 2
Command term Prove Question number H_8 Adapted from N/A

Question

Prove by mathematical induction that (22)+(32)+(42)++(n12)=(n3), where nZ,n3.

Markscheme

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

(22)+(32)+(42)++(n12)=(n3)

show true for n=3     (M1)

LHS=(22)=1 RHS=(33)=1     A1

hence true for n=3

assume true for n=k:(22)+(32)+(42)++(k12)=(k3)     M1

consider for n=k+1:(22)+(32)+(42)++(k12)+(k2)     (M1)

=(k3)+(k2)     A1

=k!(k3)!3!+k!(k2)!2!(=k!3![1(k3)!+3(k2)!]) or any correct expression with a visible common factor     (A1)

=k!3![k2+3(k2)!] or any correct expression with a common denominator     (A1)

=k!3![k+1(k2)!]

 

Note:     At least one of the above three lines or equivalent must be seen.

 

=(k+1)!3!(k2)! or equivalent     A1

=(k+13)

Result is true for k=3. If result is true for k it is true for k+1. Hence result is true for all k3. Hence proved by induction.     R1

 

Note:     In order to award the R1 at least [5 marks] must have been awarded.

 

[9 marks]

Examiners report

[N/A]

Syllabus sections

Topic 1—Number and algebra » AHL 1.15—Proof by induction, contradiction, counterexamples
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Topic 1—Number and algebra

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