Question

costita + cos3tita - 2cos2tita=0


solve the following equation​

Answer 1

Answer:

Cosθ+cos(3θ)-2cos(2θ) = 0

=> [Cosθ+cos(3θ)] -2cos(2θ) = 0

[:- cos (a) + cos (b) = 2 cos ( a+b /2)

cos ( a-b /2)

=> 2 Cos(θ+3θ /2) cos(θ-3θ /2) - 2cos(2θ) =0

=> 2 Cos (4θ/2) cos (2θ/2) - 2cos (2θ) = 0

=> 2 Cos (2θ) cos θ - 2 cos (2θ) = 0

=> 2 cos (2θ) [ cos θ - 1] = 0

2 cos (2θ) = 0 or cos θ - 1 = 0

Cos (2θ) = 0 , cos θ = 1

2θ = cos⁻¹(0) , θ = cos⁻¹(1)

2θ = π / 2 , θ = 0

θ = π / 4