Question

cos20cos40cos60cos80=?

Answer 1

hi zoom it and note it ......thanks

Answer 2

Hi,

We know that ,
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Cos x cos ( 60 - x ) cos ( 60 + x )

= 1/4 cos 3x
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Given ,

Cos 20 Cos40 Cos 60 Cos 80

= Cos 20 Cos 40 Cos 80 Cos 60

=[ Cos 20 Cos ( 60 - 20 ) Cos ( 60 + 20 )] Cos 60

= 1/4 × Cos ( 3 × 20 ) Cos 60

= 1/4 Cos 60 × Cos 60

= 1/4 × 1/2 × 1/2

= 1/ 16

I hope this helps you.

:)