The lengths of the sides of a triangle are 15m, 21m, and 28cm. What is the size of the angle facing the side 21m (correct to one decimal place)?
- 85.7Β°
-
47.5Β°
- 41.5Β°
- 41.4Β°
- 38.2Β°
The correct answer is: B
Explanation
using cosine rule,
\(cos\theta\) = \(\frac{28^2 + 15^2 - 21^2}{2\times28\times15}\)
= \(\frac{568}{840}\)
\(\theta = cos^{-1}\)
= 47.5Β°