Which calculation can be used to find the length of ac?
a. 7.8 (cos 67 degrees ) ft
b. 7.8 (tan 67 degrees ) ft
c. 7.8 (sin 23 degrees ) ft
d. 7.8 (cos 23 degrees ) ft

D. 7.8 (Cos 23 degrees ) ft

Explanation:

The Cos ratio is adjacent/hypotenuse, which in this case uses the 7.8 ft as well as length AC. We can conclude that that will be our ratio.

cos23° = AC/7.8
7.8 (cos23°) = AC

Therefore your answer is D

Side note:

If we were to use angle 67°, we would have to use the Sin ratio (opposite/hypotenuse) to use length AC as well as 7.8 ft. However Sin67° was not an option and so that angle could be ruled out.