# Trig functions that i have to memorize?

1. Mar 22, 2005

### gillgill

I am taking calculus and math 12 at the same time. Now we are doing limits of trigonometric functions, but i know nothing about it. What are some important trig functions that i have to memorize?

Ex. I have no idea how to do these
lim (tanx-sinx)/xcosx
x->0

2. Mar 22, 2005

### Zach_C

Your book probably has a table of the concepts you need such as.

d(x)sinX = cosX
d(x) cosx = -sinx
d(x) tanx = sec^2x
d(x) secx = secx tanx
d(x) cotx = -csc^2x
d(x) cscx = -cscx cot x

Are these what you were looking for?

3. Mar 22, 2005

### Jameson

To do that limit, you should use L'Hopital's Rule.

$$\lim_{x\rightarrow\infty} \frac{\tan0 - \sin0}{0*\cos0}$$ is indeterminate... you get 0/0. Differentiate the top and the bottom and try the limit again. If that doesn't work, then try it once more... If this continues to fail, use another approach.

Jameson

4. Mar 22, 2005

### whozum

Know how to find the limit of sinx/x as x-> 0, the other trig identities dont need much thought, usually rearranging or using trig identities yields you an easy limit.