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Date May 2018 Marks available 2 Reference code 18M.2.SL.TZ1.S_1
Level Standard Level Paper Paper 2 Time zone Time zone 1
Command term Solve Question number S_1 Adapted from N/A

Question

Let f(x) = ln x − 5x , for x > 0 .

Solve f '(x) = f "(x).

Markscheme

METHOD 1 (using GDC)

valid approach      (M1)

eg 

0.558257

x = 0.558       A1 N2

Note: Do not award A1 if additional answers given.

 

METHOD 2 (analytical)

attempt to solve their equation f '(x) = f "(x)  (do not accept 1 x 5 = 1 x 2 )      (M1)

eg   5 x 2 x 1 = 0 , 1 ± 21 10 , 1 x = 1 ± 21 2 , 0.358

0.558257

x = 0.558       A1 N2

Note: Do not award A1 if additional answers given.

[2 marks]

Examiners report

[N/A]

Syllabus sections

Topic 5 —Calculus » SL 5.3—Differentiating polynomials, n E Z
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Topic 2—Functions » SL 2.7—Solutions of quadratic equations and inequalities, discriminant and nature of roots
Topic 2—Functions » SL 2.10—Solving equations graphically and analytically
Topic 2—Functions
Topic 5 —Calculus

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