## Precalculus (6th Edition) Blitzer

$1.25$
Suppose $\theta = \cos^{-1} (\dfrac{\sqrt 5}{7})$ This gives: $\cos \theta=\dfrac{\sqrt 5}{7}$ Now, substitute the equation into a calculator. Therefore, we have $\cos^{-1} (\dfrac{\sqrt 5}{7})=1.25$