# Thread: derivatives of trig functions

1. ## derivatives of trig functions

find the equation of the line tangent to the graph of tanx at x=0 and x=pie/4

not really sure how to even start this problem

2. x=0 and x=pie/4 are separate problems

3. Well, if you're finding tangent lines, there's a good chance you're dealing with derivatives. The derivative of $\tan x$ is $\sec^2 x$. So you have to evaluate $\sec^2 x$ at both values of x to determine the slope m of the tangent line, and then it would probably be easiest to write the equation of the line in point-slope form using the point $(x_1, y_1)$ on the tangent graph where the line is actually tangent to the curve: $y - y_1 = m(x - x_1)$