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Date May 2021 Marks available 5 Reference code 21M.1.AHL.TZ2.7
Level Additional Higher Level Paper Paper 1 (without calculator) Time zone Time zone 2
Command term Find Question number 7 Adapted from N/A

Question

The cubic equation x3-kx2+3k=0 where k>0 has roots α, β and α+β.

Given that αβ=-k24, find the value of k.

Markscheme

α+β+α+β=k           (A1)

α+β=k2

αβα+β=-3k           (A1)

-k24k2=-3k  -k38=-3k           M1

attempting to solve -k38+3k=0 (or equivalent) for k           (M1)

k=26 =24k>0                 A1

 

Note: Award A0 for k=±26 ±24.

 

[5 marks]

Examiners report

[N/A]

Syllabus sections

Topic 2—Functions » AHL 2.12—Factor and remainder theorems, sum and product of roots
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