Question

2. The lengths of the sides of a triangle are 4cm, 5cm and 6cm. Find, in degrees to one decimal

place, the size of the largest angle of the triangle.
​

Answer 1

82.8 degrees.

Explanation:

The largest angle is opposite the longest side.

So we find the angle opposite the 6cm line using The Cosine Rule:

6^2 = 4^2 + 5^2 - 2.4.5 cos A

cos A = (6^2 - 4^2 - 5^2) / (-2*4*5)

= -5/ -40

= 0.125.

So m angle A = 82.819 degrees.