Question

Find the 90 th derivative of the function ƒ(x)=cos(x)

Answer 1

f(x) = cos x
f'(x) = -sin x
f''(x) = -cos x
f'''(x) = sin x
f''''(x) = cos x

90/4 = 22 Remainder 2
Therefore, 90th derivative of f(x) = cos x is -cos x.