Question

Cos square 30 +cos square 60+cos square 90 +2 cos 30cos 60 coe 90 =1

Answer 1

Answer:

we need to prove that cos^2 30 + cos^2 60 +cos^2 90 + cos30cos60cos90=1

LHS

cos 30= √3/2

cos 60= 1/2

cos 90= 0

substituting

(√3/2)^2+ (1/2)^2+0+0

=3+1/4

=4/4=1

=RHS

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