### Home > PC3 > Chapter 9 > Lesson 9.1.4 > Problem9-90

9-90.

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

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

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