Question Number 148388 by mathdanisur last updated on 27/Jul/21

cos40°(1 - 2cos80°) = ?

Answered by liberty last updated on 27/Jul/21

cos 40°(1−2(2cos ^2 40°−1)) = cos 40°(3−4cos ^2 40°) =3cos 40°−4cos ^3 40° =−cos 120°=(1/2)

Commented bymathdanisur last updated on 27/Jul/21

Thanks Ser