If y = cos 3x, find (frac{delta y}{delta x})
-
A.
(frac{1}{3} sin 3x) -
B.
(-frac{1}{3} sin 3x) -
C.
3 sin 3x -
D.
-3 sin 3x
Correct Answer: Option D
Explanation
y = cos 3x
Let u = 3x so that y = cos u
Now, (frac{delta y}{delta x} = 3),
(frac{delta y}{delta x} = -sin u)
By the chain rule,
(frac{delta y}{delta x} = frac{delta y}{delta u} times frac{delta u}{delta x})
(frac{delta y}{delta x} = (-sin u) (3))
(frac{delta y}{delta x} = -3 sin u)
(frac{delta y}{delta x} = -3 sin 3x)
There is an explanation video available below.