Cos 80/(cos 40+sin 40)=cos 2•40/(cos 40+sin40)=
(Cos^2 40-sin^2 40)/(cos 40+sin 40)=
(Cos 40-sin 40)(cos 40+sin 40)/(cos 40+sin 40)=cos 40-sin 40
Tg25π/4=tg(π/4+6π)=tgπ/4=1
1) примерно 0,760705
2) примерно -0,715989
G ' (x) = (3 - 2x + 1/2*x^2) ' =
= 0 - 2*1 + 1/2*2x = - 2 + x
k = g ' (x0) = g ' (3) = - 2 + 3 = 1