If y = 2x – sin2x, find dy/dx when x = π/4
-
A.
π -
B.
-π -
C.
π/2 -
D.
-π/2
Correct Answer: Option D
Explanation
y = 2x cos2x – sin2x
dy/dx = 2 cos2x +(-2x sin2x) – 2 cos2x
= 2 cos2x – 2x sin2x – cos2x
= -2x sin2x
= -2 x (π/4) sin2 x (π/4)
= -(π/2) x 1 = -(π/2)