Homework Help: Trigonometric Functionssimplify sin squared functions

1. Sep 12, 2006

ku1005

just looking at another question to do with trigonometric functions and I cant see how they simplify the follwing:
2sin^2x-3sinx-2=0 to
(2sinx+1)(sinx-2)=0
again i prob thinking sumthin really stupid...but i cant see wat!!! cheers

2. Sep 12, 2006

steve23063

The equation can be treated like a normal quadratic equation.

use substitution and replace "sinx" with "x"
2(sinx)^2-3sinx-2=0 ----> 2x^2-3x-2=0

factor the equation
2x^2-3x-2=0 = (2x+1)(x-2)

Replace "x" with "sinx"
(2x+1)(x-2)=0 -----> (2sinx+1)(sinx-2)=0

If you aren't allowed to use this method and you have to use trig identities then someone else will have to help. I'm too lazy to look up or derive the identities right now

3. Sep 12, 2006

ku1005

cheers mate...and i like ur thinkin!!!! LOL