# Math Help - derivative help

1. ## derivative help

f(x)=tan(5x)

find f'(x) and f"(x)

so i found f'(x) to be 5*sec^2(5x)

i am having trouble finding f"(x)

i thought it was 25*sec^2(5x)*tan^2(5x) but it wrong.

could i get some help with the second derivative please =)

thank you

2. Originally Posted by mybrohshi5
f(x)=tan(5x)

find f'(x) and f"(x)

so i found f'(x) to be 5*sec^2(5x)

i am having trouble finding f"(x)

i thought it was 25*sec^2(5x)*tan^2(5x) but it wrong.

could i get some help with the second derivative please =)

thank you

I don't see a factor of "2" in your coefficient. Of course, the derivative of [tex]x^2[tex] is 2x so the derivative of $5sec^2(5x)$ is 5(2 sec(5x)) times the derivative of sec(5x).