Question

2 The value of cos 20° cos 70º – sin 20°
sin 70°
(A) infinite
(B) None of these
(C) O
(D) 1​

Answer 1

U know the identity of cos i.e

Cos(a+b)= cosa cosb -sina sinb

Apply it here

U get....

Cos (20+70)

=cos 90

= 0........................... Answer option c

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