Answer
$$\sin\theta=\pm\sqrt {1-\cos^{2}\theta}$$
Work Step by Step
Start with the Pythagorean identity
$$\cos^{2}\theta+\sin^{2}\theta=1.$$
Rearrange terms and solve for $\sin\theta$:
$$\sin^{2}\theta=1-\cos^{2}\theta$$
$$\sin\theta=\pm\sqrt {1-\cos^{2}\theta}.$$
