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Date May 2021 Marks available 6 Reference code 21M.1.SL.TZ2.5
Level Standard Level Paper Paper 1 (without calculator) Time zone Time zone 2
Command term Find Question number 5 Adapted from N/A

Question

Consider the function f defined by f(x)=ln(x2-16) for x>4.

The following diagram shows part of the graph of f which crosses the x-axis at point A, with coordinates (a, 0). The line L is the tangent to the graph of f at the point B.

Find the exact value of a.

[3]
a.

Given that the gradient of L is 13, find the x-coordinate of B.

[6]
b.

Markscheme

lnx2-16=0             (M1)

e0=x2-16=1

x2=17  OR  x=±17                (A1)

a=17           A1

 

[3 marks]

a.

attempt to differentiate (must include 2x and/or 1x2-16)             (M1)

f'x=2xx2-16           A1

setting their derivative =13           M1

2xx2-16=13

x2-16=6x  OR  x2-6x-16=0 (or equivalent)           A1

valid attempt to solve their quadratic             (M1)

x=8           A1

 

Note: Award A0 if the candidate’s final answer includes additional solutions (such as x=2, 8).

 

[6 marks]

b.

Examiners report

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

Syllabus sections

Topic 5 —Calculus » SL 5.4—Tangents and normal
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