# Math Help - I can't seem to get the correct answer!

1. ## I can't seem to get the correct answer!

differentiate: $y=cos(a^3+x^3)$
my answer: $y'=-sin(a^3+x^3)(3a^2+3x^2)$
correct answer: $y'=-3x^2sin(a^3+x^3)$

I tried this multiple times and get the same answer (my answer). Either I am doing it incorrectly or the back of the book is incorrect.

2. Originally Posted by yoman360
differentiate: $y=cos(a^3+x^3)$
my answer: $y'=-sin(a^3+x^3)(3a^2+3x^2)$
correct answer: $y'=-3x^2sin(a^3+x^3)$

I tried this multiple times and get the same answer (my answer). Either I am doing it incorrectly or the back of the book is incorrect.
$a^3$ represents a constant ...

$y = \cos(a^3 + x^3)$

$y' = -\sin(a^3 + x^3) \cdot 3x^2$