Sections:

Trigonometric Identities and Equations, Page 22

Examples (continued)

Example 2:

Find the value of sin 15° using the sine Half-Angle Identity (round your answer to four decimal places).

Use the formula sinα/2 = ± square root [(1 - cosα)/2] and let alpha= 30°.

sin30/2 = ± square root [(1 - cos30)/2]; sin15 = ± square root [(1 - .866)/2]; sin15 = .2588

Since 15° is in Quadrant I, you should only be interested in the positive value.