If y = 2xcos2x – sin2x, find dy/dx when x = π/4
- π
-
-π
- π/2
- -π/2
The correct answer is: B
Explanation
y = 2x cos2x - sin2x
dy/dx = 2 cos2x +(-2x. 2sin2x) - 2cos2x
= 2 cos2x - 2x sin2x - cos2x
= -2x 2sin2x
= -4 x (π/4) sin2 x (π/4)
= -(π) x 1 = - π
There is an explanation video available .