# Thread: Hello, I Really Need Help With Trigonometric Identities

1. ## Hello, I Really Need Help With Trigonometric Identities

Hello, i need help with trigonometric identities, if anyone can help me, please add me to your msn messenger, my e-mail is falcolneye@hotmail.com, i need someone to help me!!!

THANKYOU!

2. No, that doesn't make any sense.

Post your problems and show us what you've done.

Make it nice and understandable with math formulae. (See my signature.)

3. ## well here's my first problem

cos琊cos球+sin琊sin球+sin琊+cos球+sin球cos琊=1

solve this using reciprocal identities, quotient identities, pythagorean identities

4. cos琊cos球+sin琊sin球+sin琊+cos球+sin球cos琊=1
$\displaystyle cos^2x(cos^2y+sin^2y)+sin^2xsin^2y+sin^2x+cos^2y = 1$
$\displaystyle cos^2x+sin^2x+sin^2xsin^2y+cos^2y = 1$
$\displaystyle sin^2xsin^2y+cos^2y = 0$
$\displaystyle (sinxsiny)^2 = -cos^2y$

Since $\displaystyle (sinxsiny)^2 \geq 0$ and $\displaystyle -cos^2y \leq 0$
$\displaystyle (sinxsiny)^2 = -cos^2y = 0$
$\displaystyle y = \frac{\pi}{2} +n\pi$
$\displaystyle x = m\pi$
where n,m are integers.