Q. 13 B5.0( 1 Vote )

Show by an example that

cos C + cos D ≠ cos (C + D)

Answer :

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

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

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

L.H.S. R.H.S

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