### Home > PC3 > Chapter Ch8 > Lesson 8.3.4 > Problem8-138

8-138.

Rewrite each expression as the sine, cosine, or tangent of an angle.

1. $\sin\left(\frac{3\pi}{2}\right)\cos\left(\frac{\pi}{7}\right)-\cos\left(\frac{3\pi}{2}\right)\sin\left(\frac{\pi}{7}\right)$

Look at the angle difference formula for sine.

2. $\cos\left(\frac{\pi}{3}\right)\cos\left(\frac{3\pi}{10}\right)-\sin\left(\frac{\pi}{3}\right)\sin\left(\frac{3\pi}{10}\right)$

Look at the angle sum formula for cosine.

3. $\frac { \operatorname { tan } ( 203 ^ { \circ } ) - \operatorname { tan } ( 6 ^ { \circ } ) } { 1 + \operatorname { tan } ( 203 ^ { \circ } ) \operatorname { tan } ( 6 ^ { \circ } ) }$

Look at the angle difference formula for tangent.