JAMB Mathematics 2020 Objective — Question 7

Question 7 of 40 from the Joint Admissions and Matriculation Board (JAMB) Mathematics 2020 Objective paper, with the correct answer and a full explanation.

If y = (1-2x)^3, find the value of dy/dx at x=-1.

A. -6
B. 57
C. -54Correct
D. 27

Explanation

Let u=1-2x, du/dx=-2. y=u^3, dy/du=3u^2. dy/dx=3u^2 x -2=-6u^2=-6(1-2x)^2. At x=-1: -6(1-2(-1))^2=-6(3)^2=-54.

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