Question

tan 20 degree × tan 40 degree × tan 80 degree = tan 60 degree

Answer 1

$formula \: based \: ques \\ tan \: x \:tan(60 - x)tan(60 + x) \\ = tan3x \\ tan \: 20 \:tan(60 - 20)tan(60 + 20) = tan \: 3(20) \\ = \tan(60) \\ other \: formuli \\ sin \: x \: sin(60 - x)sin(60 + x) = \\ \frac{1}{4} sin \: 3x \\ cos \: x \: cos(60 - x)cos(60 + x) = \frac{1}{4} cos3x$