Chapter 7 - Section 7.3 - Double-Angle, Half-Angle, and Product-Sum Formulas - 7.3 Exercises - Page 560: 2

Half-Angle, $\pm\sqrt{\frac{1-\cos u}{2}}$

If we know the value of $\cos x$ and the quadrant in which $x/2$ lies, we can find the value of $\sin(x/2)$ by using the Half-Angle Formula for Sine. State the formula: $\sin(x/2)=\pm\sqrt{\frac{1-\cos u}{2}}$.