Question

use a calculator. round to the nearest tenth. find $\cos^{-1}(0.7866)$.

Explanation:

Step1: Use calculator for arccos

Using a calculator, find $\cos^{-1}(0.7866)$. Ensure calculator is in degree mode (since the answer is expected in degrees, likely).
$\cos^{-1}(0.7866) \approx 38.2^\circ$ (calculator input: arccos(0.7866))

Step2: Round to nearest tenth

The value is already to the nearest tenth as 38.2 (the first decimal place is 2, and the next digit is less than 5, so no change).

Answer:

38.2