Date | May Specimen paper | Marks available | 3 | Reference code | SPM.1.AHL.TZ0.9 |
Level | Additional Higher Level | Paper | Paper 1 (without calculator) | Time zone | Time zone 0 |
Command term | Find | Question number | 9 | Adapted from | N/A |
Question
The function ff is defined by f(x)=e2x−6ex+5,x∈R,x⩽a. The graph of y=f(x) is shown in the following diagram.
Find the largest value of a such that f has an inverse function.
[3]
a.
For this value of a, find an expression for f−1(x), stating its domain.
[5]
b.
Markscheme
attempt to differentiate and set equal to zero M1
f′(x)=2e2x−6ex=2ex(ex−3)=0 A1
minimum at x=ln3
a=ln3 A1
[3 marks]
a.
Note: Interchanging x and y can be done at any stage.
y=(ex−3)2−4 (M1)
ex−3=±√y+4 A1
as x⩽ln3, x=ln(3−√y+4) R1
so f−1(x)=ln(3−√x+4) A1
domain of f−1 is x∈R, −4⩽x<5 A1
[5 marks]
b.
Examiners report
[N/A]
a.
[N/A]
b.