Q. 163.7( 3 Votes )


Evaluate cos (40

Answer :


Consider: cos (40 o + θ) – sin (50 o - θ ) +
= cos [(90° - 50° ) + θ ] – sin(50° - θ ) +

= cos [90° - (50° - θ)] – sin(50° - θ ) +

= sin (50° - θ) – sin(50° - θ ) + (1/1)

( sin 2 θ + cos 2 θ = 1)
=
0 + 1
= 1.

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