Q13 of 268 Page 4

Show by an example that
cos C + cos D ≠ cos (C + D)

Let C = 60^o and D = 30^o, then

L.H.S. = cos C + cos D = cos 60^o + cos 30^o

R. H. S. = cos (C+D) = cos (60^o + 30^o) = cos 90^o= 0

L.H.S. R.H.S

If sin (A – B) = 1/2, cos(A + B) = 1/2; 0^o<A+B<90^o; A > B, find A and B.

Show by an example that

cos A – cos B ≠ cos (A – B)

Show by an example that

sin A + sin B ≠ sin (A + B)

Show by an example that

sin A – sin B ≠ sin (A – B)

Show by an example thatcos C + cos D ≠ cos (C + D)