Question

Пожалуйста только 129 (

Answer 1

$cos(90- alpha )=sin alpha ; ,; ; ; sin(90- alpha )=cos alpha \\1)quad 2cos40cdot cos50=2cos40cdot cos(90-40)=2cos40cdot sin40=\\=sin80=sin(90-10)=cos10\\2)quad 2sin25cdot sin65=2sin25cdot sin(90-25)=2sin25cdot cos25=\\=sin50(; libo; =cos40)\\3)quad sin2 alpha +(sin alpha -cos alpha )^2=$

$=2sin alpha cdot cos alpha +(sin^2 alpha -2sin2 alpha cdot cos alpha +cos^2 alpha )=\\=sin^2 alpha +cos^2 alpha =1$

$4)quad cos4 alpha +sin^22 alpha =(cos^22 alpha -sin^22 alpha )+sin^22 alpha =cos^22 alpha$