Q2 of 90 Page 9

Prove that :

i.


ii.


iii.


i. We know, 2 sin A sin B = cos (A – B) – cos (A + B)






= cos 60° - cos 90°




Hence Proved


ii. We know, 2 cos A cos B = cos (A + B) + cos (A – B)






= cos 90° + cos 60°




Hence Proved


iii. We know, 2 sin A cos B = sin (A + B) + sin (A – B)





= sin 90° + sin 60°




Hence Proved


More from this chapter

All 90 →
1

Express each of the following as the sum or difference of sines and cosines:

(i) 2 sin 3x cos x


(ii) 2 cos 3x sin 2x


(iii) 2 sin 4x sin 3x


(iv) 2 cos 7x cos 3x

 3

Show that:

i.


ii.

4

Prove that:

 5

Prove that: