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Date November Example question Marks available 4 Reference code EXN.1.AHL.TZ0.15
Level Additional Higher Level Paper Paper 1 Time zone Time zone 0
Command term Hence and Find Question number 15 Adapted from N/A

Question

Consider the function fx=-ax2+x+a, a+.

For a>0 the curve y=fx has a single local maximum.

Find f'x.

[2]
a.

Find in terms of a the value of x at which the maximum occurs.

[2]
b.

Hence find the value of a for which y has the smallest possible maximum value.

[4]
c.

Markscheme

* This sample question was produced by experienced DP mathematics senior examiners to aid teachers in preparing for external assessment in the new MAA course. There may be minor differences in formatting compared to formal exam papers.

f'x=-2ax+1×12×-ax2+x+a-12

 

Note: M1 is for use of the chain rule.

 

=-2ax+12-ax2+x+a         M1A1

 

[2 marks]

a.

-2ax+1=0         (M1)

x=12a       A1

  

[2 marks]

b.

Value of local maximum =-a×14a2+12a+a         M1A1

=14a+a

This has a minimum value when a=0.5         (M1)A1

  

[4 marks]

c.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.

Syllabus sections

Topic 5—Calculus » SL 5.6—Stationary points, local max and min
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Topic 5—Calculus » AHL 5.9—Differentiating standard functions and derivative rules
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