Date | May 2021 | Marks available | 2 | Reference code | 21M.2.SL.TZ1.9 |
Level | Standard Level | Paper | Paper 2 | Time zone | Time zone 1 |
Command term | Show that | Question number | 9 | Adapted from | N/A |
Question
Consider the function f defined by f(x)=90e-0.5x for x∈ℝ+.
The graph of f and the line y=x intersect at point P.
The line L has a gradient of -1 and is a tangent to the graph of f at the point Q.
The shaded region A is enclosed by the graph of f and the lines y=x and L.
Find the x-coordinate of P.
Find the exact coordinates of Q.
Show that the equation of L is y=-x+2 ln 45+2.
Find the x-coordinate of the point where L intersects the line y=x.
Hence, find the area of A.
The line L is tangent to the graphs of both f and the inverse function f-1.
Find the shaded area enclosed by the graphs of f and f-1 and the line L.
Markscheme
Attempt to find the point of intersection of the graph of f and the line y=x (M1)
x=5.56619…
=5.57 A1
[2 marks]
f'(x)=-45e-0.5x A1
attempt to set the gradient of f equal to -1 (M1)
-45e-0.5x=-1
Q has coordinates (2 ln 45, 2) (accept (-2 ln 145, 2) A1A1
Note: Award A1 for each value, even if the answer is not given as a coordinate pair.
Do not accept ln 145-0.5 or ln 450.5 as a final value for x. Do not accept 2.0 or 2.00 as a final value for y.
[4 marks]
attempt to substitute coordinates of Q (in any order) into an appropriate equation (M1)
y-2=-(x-2 ln 45) OR 2=-2 ln 45+c A1
equation of L is y=-x+2 ln 45+2 AG
[2 marks]
x=ln 45+1(=4.81) A1
[1 mark]
appropriate method to find the sum of two areas using integrals of the difference of two functions (M1)
Note: Allow absence of incorrect limits.
∫5.566…4.806…(x-(-x+2 ln 45+2))dx+∫7.613…5.566…(90e-0.5x-(-x+2 ln 45+2))dx (A1)(A1)
Note: Award A1 for one correct integral expression including correct limits and integrand.
Award A1 for a second correct integral expression including correct limits and integrand.
=1.52196…
=1.52 A1
[4 marks]
by symmetry 2×1.52… (M1)
=3.04 A1
Note: Accept any answer that rounds to 3.0 (but do not accept 3).
[2 marks]