trig equations help?

**eh501** · November 24th 2008, 06:10 PM

I'm stuck on these questions:

1. Find theta in the interval 0 <theta<360 that satisfies the equation $cos^2theta=sin^2theta+1$

2. $2cos^2x+2cosx-1=0$

**Moo** · November 24th 2008, 11:22 PM

Hello,

Originally Posted by eh501

I'm stuck on these questions:

1. Find theta in the interval 0 <theta<360 that satisfies the equation $cos^2theta=sin^2theta+1$

recall the identity cos²x+sin²x=1.

hence your equation becomes :
$1-\sin^2 \theta=\sin^2 \theta+1$
which simplifies to :
$2 \sin^2 \theta=0$
$\sin \theta=0$

2. $2cos^2x+2cosx-1=0$

Let $X=\cos(x)$
Solve the quadratic
and then find the solutions ^^

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