Verify that 1 + cos 2 theta / 2 cos theta = cos theta is an identity

Answer and Step-by-step explanation:

We want to verify that (1 + cos(2θ)) / 2cos(θ) = cos(θ).

Let's focus on the left side. Look at cos(2θ). This is an identity, so remember that cos(2θ) = cos²θ - sin²θ. Also, look at the 1. Remember that sin²θ + cos²θ = 1, so plug both of these expressions into our equation:

(1 + cos(2θ)) / 2cos(θ) =? cos(θ)

((sin²θ + cos²θ) + (cos²θ - sin²θ)) / 2cos(θ) =? cos(θ)

2cos²θ / 2cosθ =? cosθ

cosθ = cosθ

Thus, we have proved this is an identity.

(1 + cos(2theta))/2cos(theta)

cos(2theta) = 2cos²(theta) - 1

(1 + 2cos²(theta) - 1)/2cos(thetal

2cos²(theta)/2cos(theta)

cos(theta)