If y = 3 cos 4x, dy/dx equals?
...If y = 3 cos 4x, dy/dx equals?
6 sin 8x
-24 sin 4x
12 sin 4x
-12 sin 4x
Correct answer is D
y = 3 cos 4x
Applying product rule:
dydx = udvdx + vdudx
Where u = 3 and v = cos 4x
dudx of 3 = 0 and
dvdx of cos 4x = -4sin 4x
dydx = 3 × -4 sin 4x + cos 4x × 0
dydx = -12 sin 4x