# Math Help - chain rule

1. ## chain rule

Find the derivative of the function. y = a9 + (cos(x))9

It keeps saying its wrong... heres what i did:

sum rule,

derivative of a^9 + derivative of (cos(x))9

9a^8 + ..........

outside function = x^9
derivative of outside function= 9x^8
inside function= cos(x)
derivative of inside function= -sin(x)

......... 9(cos[x])^8 * -sin(x)

9a^8 + (9(cos[x])^8 * -sin(x))

2. Originally Posted by Evan.Kimia
Find the derivative of the function. y = a9 + (cos(x))9

It keeps saying its wrong... heres what i did:

sum rule,

derivative of a^9 + derivative of (cos(x))9

9a^8 + ..........

outside function = x^9
derivative of outside function= 9x^8
inside function= cos(x)
derivative of inside function= -sin(x)

......... 9(cos[x])^8 * -sin(x)

9a^8 + (9(cos[x])^8 * -sin(x))

if $y$ is a function of $x$, then $a^9$ is probably a constant ... the derivative of a constant is 0