Question

In △DEF, d = 25 in., e = 28 in., and f = 20 in. Find m∠F. Round your answer to the nearest tenth.

Answer 1

∠F ≈ 43.9°

Explanation:

The Law of Cosines is used to find an angle when all triangle sides are known.

f² = d² +e² -2de·cos(F)

cos(F) = (d² +e² -f²)/(2de) = (25² +28² -20²)/(2·25·28) = 1009/1400

F = arccos(1009/1400)

F ≈ 43.9°