Date | May 2021 | Marks available | 2 | Reference code | 21M.2.AHL.TZ2.12 |
Level | Additional Higher Level | Paper | Paper 2 | Time zone | Time zone 2 |
Command term | Show that | Question number | 12 | Adapted from | N/A |
Question
A function is defined by .
A function is defined by .
Show that is an even function.
By considering limits, show that the graph of has a horizontal asymptote and state its equation.
Show that for .
By using the expression for and the result , show that is decreasing for .
Find an expression for , justifying your answer.
State the domain of .
Sketch the graph of , clearly indicating any asymptotes with their equations and stating the values of any axes intercepts.
Markscheme
EITHER
R1
OR
a sketch graph of with line symmetry in the -axis indicated R1
THEN
so is an even function. AG
[1 mark]
as A1
so the horizontal asymptote is A1
[2 marks]
attempting to use the quotient rule to find M1
A1
attempting to use the chain rule to find M1
let and so and
M1
A1
A1
AG
[6 marks]
EITHER
for (A1)
so A1
OR
and A1
A1
THEN
R1
Note: Award R1 for stating that in , the numerator is negative, and the denominator is positive.
so is decreasing for AG
Note: Do not accept a graphical solution
[3 marks]
M1
A1
A1
domain of is and so the range of must be
hence the positive root is taken (or the negative root is rejected) R1
Note: The R1 is dependent on the above A1.
so A1
Note: The final A1 is not dependent on R1 mark.
[5 marks]
domain is A1
Note: Accept correct alternative notations, for example, or .
Accept if correct to s.f.
[1 mark]
A1A1A1
Note: A1 for correct domain and correct range and -intercept at
A1 for asymptotic behaviour
A1 for
Coordinates are not required.
Do not accept or other inexact values.
[3 marks]