2 cos^2 ? + cos ? = 1 HELP

Question

I can't seem to do this and i appreciate the help 

Answer 1

2 cos^2 θ + cos θ = 1 is to be solved.

 

Let x = cos θ and rewrite the given equation as 2x² +x - 1= 0.

 

Factoring gives (2x-1)(x+1) = 0 so x = ½ or x = -1 using the Zero Product Property.

 

Replace x and see that we now have cos θ = -1 or cos θ = ½.

 

I will let you take it from here to solve for theta.

Answer 2

Also try trial and error using the unit circle. Please memorize the unit circle. It will save you so much time!

 

I will get you started

 

2cos²x + cosx = 1

 

2cos²0 + cos(0) = 1

2(1)¹ + 1 ≠ 1

 

I didn't find the answer yet because I want you to take it from here on.