# Math Help - trigo problem no. 22

1. ## trigo problem no. 22

p198 q10 reex9
thanks

2. Originally Posted by afeasfaerw23231233
p198 q10 reex9
thanks

Your answers are clearly wrong since they don't satisfy the original equations.

Your mistake is in forgetting that $\theta - \phi = \pi$ is only one of several possible solutions to $\cos (\theta - \phi) = -1$. Other solutions include $-\pi$ .....

When you solve

$\theta - \phi = - \pi$ .... (1)

$\theta + \phi = \frac{5 \pi}{3}$ .... (2)

simultaneously, you get the books answer (which is correct by the way).