If y = (1 – 2x)(^3), find the value of dy/dx at x = -1
- A.
57 - B.
27 - C.
-6 - D.
-54
Correct Answer: Option D
Explanation
y = (1 – 2x)(^3)
let u = 1-2x
du/dx = -2
∴y = u(^3)
dy/du = 3u(^2)
But dy/dx = du/dx * dy/du
= -2 * 3u(^2)
= -6u(^2)
= -6(1-2x)(^2)
At x = -1: dy/dx = -6(1 – 2(-1))(^2)
dy/dx = -6(1 + 2)(^2)
= -6 * 3(^2)
= -6 * 9
= -54