CPM Homework Help : PC3 Problem 9-90

Calculate the exact value of $\sec\left(a+b\right)$ where $cos(a) = \frac { 3 } { 5 }$ , $a$ is in Quadrant IV, $\tan(b) = −\frac { 12 } { 5 }$ , and $b$ is in Quadrant II. Hint: Calculate $\cos(a+b)$ .

Hint:

Sketch two triangles for this situation. One for angle $a$ and one for angle $b$ .

More Help:

$\cos(a + b) = \cos(a)\cos(b) − \sin(a)\sin(b)$