Calc Help!

[ecoli]

[math]\lim_{h\to\.0} \frac{tan3(x+h) - tan(3x)}{h} [/math]

 

I know the answer is [math]3sec^2(3x) [/math]. But I'm having a very difficult time finding why, could anyone help me? What trig identities do you need?

 

Thanks in advanced!

[ecoli]

Never mind, guys. I got it.