Half-Angle Calculator

Published on: March 16, 2025

Compute sin(θ/2), cos(θ/2) or tan(θ/2) using their half-angle identities.

Step-by-step method

  1. Identify what is given.
  2. Write the correct half-angle identity.
  3. Substitute the values and calculate.

Formulas:

Formula: sin(θ/2)

sin(θ/2)=
1 − cosθ
2

Formula: cos(θ/2)

cos(θ/2)=
1 + cosθ
2

Formula: tan(θ/2)

tan(θ/2)=
1 − cosθ
1 + cosθ

Example 1: sin(θ/2) with θ = 60°

Step 1 - Identify what is given.

In this problem: The given angle is θ = 60°.

θ=60°

Step 2 - Write the correct half-angle identity.

In this problem: Use the identity: sin(θ/2) = √((1 − cosθ) / 2).

sin(θ/2)=
1 − cosθ
2

Step 3 - Substitute the values and calculate.

In this problem: First find cosθ = cos(60°) = 0.5, then substitute and compute.

sin(θ/2)=
1 − 0.5
2
=√0.25=0.5

Final answer: sin(θ/2) = 0.5

Example 2: tan(θ/2) with θ = 30°

Step 1 - Identify what is given.

In this problem: The given angle is θ = 30°.

θ=30°

Step 2 - Write the correct half-angle identity.

In this problem: Use the identity: tan(θ/2) = √((1 − cosθ) / (1 + cosθ)).

tan(θ/2)=
1 − cosθ
1 + cosθ

Step 3 - Substitute the values and calculate.

In this problem: First find cosθ = cos(30°) = 0.8660254, then substitute and compute.

tan(θ/2)=
1 − 0.8660254
1 + 0.8660254
=√0.07179677=0.26794919

Final answer: tan(θ/2) = 0.26794919