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.

## Answer this Question

## Related Questions

- Trigonometry - I am having problems with proving identities that has a number ...
- Trig - Which expression equivalent to: cos(theta + pi/2). A)cos theta B)-cos ...
- Trigonometry - determine real numbers a and b so that the expression 8sin^2(...
- trigonometry - can you correct the rest for me please? Express each as a ...
- trigonometry - can you correct the rest for me please? Express each as a ...
- Calculus - I wanted to confirm that I solved these problems correctly (we had to...
- math(Trigonometry) - sin 2 theta + cos theta = 0 so, we use sin 2 theta = 2 sin ...
- Trigonometry - Thank you STEVE!!!!! Suppose that Cos (theta) = 1/square root 2 ...
- Trigonometry - State the amplitude of the following functions: a) y = cos theta ...
- Mathamatics - Solve the following trigonometry identities. a) 1-cos2(theta) = ...

More Related Questions