Question

1
s. Prove that cos 20° cos 40° cos 60° cos 80°
16​

Answer 1

Answer:

$we \: know \\ </p><p>cosx \: cos(60 - x) \: cos(60 + x) = \frac{1}{4} cos3x \\ now \\ cos20 \: cos40 \: cos60 \: cos80 \\ \frac{1}{2} cos20 \: cos40 \: cos80 \\ = \frac{1}{2} cos20 \: cos(60 - 20) \: cos(60 + 20) \\ = \frac{1}{2} \times \frac{1}{4} cos60 \\ = \frac{1}{8} \times \frac{1}{2} \\ = \frac{1}{16}$

Answer 2

I don't know what I don't know what you think about it is not