# Thread: Help with Trigonometric Identities

1. ## Help with Trigonometric Identities

$\displaystyle sec^2{x}+tan^2{x}sec^2{x}=sec^4{x}$

So far I have changed everything to fractions using the quotient properties, but I have no idea where to go next.

2. Use the identity $\displaystyle \displaystyle \tan^2{x} + 1 = \sec^2{x} \implies \tan^2{x} = \sec^2{x} - 1$.

Substitute this into the LHS and simplify.

3. Sorry, but what does LHS stand for?

4. Originally Posted by toeknee
Sorry, but what does LHS stand for?
Left Hand Side. Meaing if we have the expression a + 1 = b then the LHS is a + 1.

-Dan

5. Left Hand Side

6. You can still use the Pythagorean property for $\displaystyle tan^2{x}sec^2{x}$?

7. Surely $\displaystyle \displaystyle \tan^2{x}\sec^2{x} = (\sec^2{x} - 1)\sec^2{x}$...

8. I thought because it was one term, you couldn't, but I guess not. Thanks a lot for your help. Kind of fitting that your name is Prove It.