what you have is
cosθ + 1 = 2cos^2θ - 1
2cos^2θ - cosθ - 2 = 0
so, solve that quadratic for cosθ and pick the choice.
Solve 2cos^2θ/2 = cos2θ for 0º≤θ≤360º. (Hint: Graph each side of the equation and find the points of intersection.)
A) ≈73.8º; 260.4º
B) ≈141.3º; 218.7º
C) ≈225.7º; 315.8º
D) ≈51.7º; 138.2º
1 answer
1 answer