1) x(2x-5)=0
x=0 and 2x=5
x=2.5
2) x(2-5x)=0
x=0 and -5x=-2
x=2/5
3)y²-2y-8-2y+8=0
y²-4y=0
y(y-4)=0
y=0 and y = 4
в=-3а
(5а+3в)/(а-9а)=8а/(-8а)=-1