1) 2х = 4/3 * (х + 15) 2) 2/3 * (10 - х) = - 12
2х = 4/3х + 4/3*15 2/3*10 - 2/3х = - 12
2х - 1 1/3х = 20 20/3 + 12 = 2/3х
2/3х = 20 18 2/3 = 2/3х
х = 20 : 2/3 = 20 * 3/2 х = 56/3 : 2/3 = 56/3 * 3/2
х = 60/2 = 30 х = 168/6 = 28
3) - 1/4 * (5х - 7) = 6
- 1/4*5х - 1/4 * (- 7) = 6
- 5/4х + 7/4= 6
- 1,25х = 6 - 1,75
- 1,25х = 4,25
х = 4,25 : (-1,25)
х = - 3,4
а=3/4
у=3/4х^2=5-х
отсюда 3х^2+4х-20=0
Д=16+240=256
х1=(-4+16)/6=2
х2=(-4-16)/6=-10/3
подставляем в уравнения и находим у
у2=5-(-10/3)=8 1/3
ответ:(-3 1/3;8 1/3)