Posted by **aaa** on Monday, February 4, 2013 at 3:35am.

2cos^2 theta + 5 sin theta - 4 = 0

- math(Trigonometry) -
**Steve**, Monday, February 4, 2013 at 5:22am
2(1-sin^2) + 5sin - 4 = 0

2sin^2 - 5sin + 2 = 0

(2sin-1)(sin-2) = 0

sin = 1/2 or 2

...

- math(Trigonometry) -
**aaa**, Monday, February 4, 2013 at 6:08am
can give me a further and detail explanation where did the theta on the 5 and the formula on changing the cos theta.

- math(Trigonometry) -
**Steve**, Monday, February 4, 2013 at 10:15am
you know that cos^2 = 1-sin^2

the rest is just algebra I

I dropped the thetas just for ease of typing.

Naturally, sin can never be 2, so that's a non-solution, even though it does satisfy the original equation.

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