Asked by adele

i need to factorise 4 cos squared theta + 2 cos theta - 1

15 years ago

Answered by Damon

I can not factor
4 x^2 + 2x -1

15 years ago

Answered by drwls

Let's let cos theta = x.
You want to factor
4x^2 + 2x -1
Use the standard quadratic equation.

The roots are
x = (1/8)[-2 +/-sqrt20]
= (1/4)[-1 +/-sqrt5]
The factors are
(x - (1/4)(1 - sqrt5)][x - (1/4)(1 + sqrt5)]

Substitute back costheta for x if you with.

Check my work for algebra mistakes.

15 years ago

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