We are asked to prove tan(θ / 2) = sin θ / (1 + cos θ). In this case, tan θ is equal to sin θ / cos θ. we can apply this to the equality. sin θ is equal to square root of (1-cos θ)/2 while cos θ is equal to <span>square root of (1 + cos θ)/2. Hence, when we replace cos </span><span>θ with </span>square root of (1-cos θ)/2, we can prove already.
