#### Johnny Blaze

##### New member

- Joined
- Aug 8, 2019

- Messages
- 10

Here's my working

Since angle A = 90

Angle (B + C) = 90

Sin (B + C) = Sin 90 = 1

Cos (B + C) = Cos 90 = 0

Sin (B + C) = Sin B Cos C + Cos B Sin C

Cos (B + C) = Cos B Cos C - Sin B Sin C

0 = Cos B Cos C - 0.2

Cos B Cos C = 0.2

2 Cos B Cos C = 0.4

Cos (B + C) + Cos (B - C) = 0.4

0 + Cos (B - C) = 0.4

Cos (B - C) = 0.4 = 2/5

Sin (B - C) = Sin B Cos C - Cos B Sin C = 5a/2

Cos (B - C) = Cos B Cos C + Sin B Sin C = 2/5

Now I'm really stuck here. Please help!