Question

Prove that
Cos20-cos40-cos80=0

Answer 1

$cos20^{o}-cos40^{o}-cos80^{o}\\cos20^{o}-(cos40^{o}+cos80^{o})\\cos20^{o}-(2cos((40+80)/2 )^{o}cos((80-40)/2 )^{o})\\cos20^{o}-(2cos60^{o}cos20^{o})\\cos20^{o}(1-2cos60^{o})\\cos20^{o}(1-2(\frac{1}{2}} )\\cos20^{o}(0)\\=0$

Answer 2

Answer:

prove that cos20°-cos40°-cos80°=0

cos20°-cos40°-cos80°

Take '-' common

cos20°-(cos40°+cos80°)

cos20°(2cos40+80/2×cos40-80/2)

cos20°-(1×cos20°)

cos20°-cos20°=0

HENCE PROVED....IF YOU HAVE UNDERSTOOD THIS ABOVE PROBLEM PLEASE LIKE.

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