Help!...with trig

[Wes]

I need all possible solutions for x:

2 cos^2 x - sin x - 1 = 0

Thanks!

 

[ChaoticLlama]

Here's a hint

Make a substitution for cos²x with this identity

cos²x + sin²x = 1

 

[stapel]

...and when you've made that substitution, note that you have a quadratic in sin(x). Solve that for the values of sine, and then solve the two resulting equations for the values of x.

Eliz.

 

[pav]

ok as we've said on MMB

Sin^2+Cos^2=1

thus

Cos^2=1-Sin^2

2(1-Sin^2)(x)-Sin(x)-1=0

then substitute y=sin(x) and solve