Question

Prove: cos20o x cos40o x cos60o x cos80o= 1/16

Answer 1

cos20°×cos40°×cos60°×cos80°
={1/2sin20°}2sin20°cos20°cos40°cos60°cos80°
={1/2sin20°}sin40°cos40°cos60°cos80°
={1/4sin20°}2sin40°cos40°cos60°cos80°
={1/4sin20°}sin80°cos60°cos80°
={1/8sin20°}2sin80°cos80°1/2
={1/16sin20°}cos160°
=1/16

hence proved


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Answer 2

DEAR STUDENT,

Kindly check the attached papers for a detailed solution along with step by step elaboration to reach our final solution that is our final desired or required answer to this query that is completely proved.

$\boxed{\bf{\underline{L.H.S. = R.H.S.}}}$

Which is the required proof or solution process for this type of query.

Hope this helps you and solves your doubts for applying trigonometric identifies to reach a proper solution or a proof!!!!!