F(x)=2cosx/2+4sinx/4
f'(x)=-2*1/2sinx+4*1/4cosx= cosx-sinx
f'(x)=0 cosx-sinx=0 sinx=cosx sinx/cosx=1
tgx=1 x=π/4+πn n∈Z
(2х-y)^2-9m^2 = (2х-y)^2-(3m)^2 = (2х-y-3m)(2х-y+3m)
2x-3x+21≤3
-x≤-18 *(-1)
x≥18
Ответ: [18; +∞)
-x=24+4x
4x+x=-24
5x=-24
x=-24:5
x=-4,8