Question

Question #97001

Answer 1

see below

Explanation:

Use formula `cosx+cosy=2cos (1/2(x+y))cos(1/2(x-y))`
`cos 70 +cos 20=2 cos (1/2 (70+20))cos(1/2 (70-20))`

`=2cos(90/2) cos(50/2)`

`=2cos45cos25`