Q2 of 90 Page 8

Prove that :

cos 100° + cos 20° = cos 40°

Take L.H.S:


cos 100° + cos 20°





= 2 cos 60° cos 40°



= cos 40°


= R.H.S


Hence Proved


More from this chapter

All 90 →
1

Express each of the following as the product of sines and cosines:

i. sin 12x + sin 4x


ii. sin 5x – sin x


iii. cos 12x + cos 8x


iv. sin 2x + cos 4x

 2

Prove that :

sin 38° + sin 22°= sin 82°

 2

Prove that :

sin 50° + sin 10° = cos 20°

 2

Prove that :

sin 23° + sin 37° = cos 7°