-4(3 - х) = 2х + 7
- 12 + 4х = 2х + 7
-12 - 7= 2х- 4х
-19= -2х
х= -19 : ( -2)
х= 9,5
(Tg(t)+ctg(t))sin(t)/tg=sin^-1
(sin(t)/cos(t)+cos(t)/sin(t))×sin(t)÷tg(t)=
Sin^2(t)+cos^2(t)÷cos(t)sin(t)×sin(t) / tg(t).
Sin^2(t)+cos^2(t)=1
Sin(t)/sin(t)cos(t)÷tg(t)=1/cos(t)×cos(t)/sin(t)=1/sin(t)=sin^-1(t)
Доказано.