Question

How to solve this problem 0 <= 0 < 2pi: cos4 (theta) + cos5 (theta) = 0

Answer 1

Answer:

cos(theta)=0. cos(θ)=0. Take the inverse cosine of both sides of the equation to extract θ from inside the cosine. θ=arccos(0) The exact value of arccos(0) is π2 .

Answer 2

2cos2θ=cosθ

⇒2cos2θ−cosθ=0

⇒cosθ(2cosθ−1)=0

⇒cosθ=0