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)?
A
85.7°
B
47.5°
C
41.5°
D
41.4°
E
38.2°
Verified Correct Answer: B.
Step-by-Step Mathematical Solution
using cosine rule,
\(cos\theta\) = \(\frac{28^2 + 15^2 - 21^2}{2\times28\times15}\)
= \(\frac{568}{840}\)
\(\theta = cos^{-1}\)
= 47.5^\circ
Source: Myschool Past Questions Archive (Record #41965)