# Math Help - Trigonometric equations

1. ## Trigonometric equations

Been having problem with a few questions from my review for solving trig equations

$
Cos2X(Sin2x-1)=0
$

and

$
2Cos^2x-cosx-1=0
$

2. Originally Posted by nightrider456
Been having problem with a few questions from my review for solving trig equations

$
Cos2X(Sin2x-1)=0
$

and

$
2Cos^2x-cosx-1=0
$
$\cos(2x)[\sin(2x)-1]=0$

set each factor equal to 0 and solve ...

$\cos(2x) = 0$

$2x = \frac{\pi}{2}$ , $2x = \frac{3\pi}{2}$ , ...

$\sin(2x) = 1$

$2x = \frac{\pi}{2}$ , $2x = \frac{5\pi}{2}$ , ...

$2\cos^2{x}-\cos{x}-1=0$

$(2\cos{x} + 1)(\cos{x} - 1) = 0$

same drill ... set each factor equal to 0 and solve.