A,x+y=13->x=13-y
xy=36 -->(13-y)y=36
-y[SUP]2[/SUP]+13y-36=0
Y=9 hoac y=4
B,x-y=3 ->x=3+y
->xy=10->(3+y)y=10
Y[SUP]2[/SUP]+3y-10=0
Y=2 hoặc y=-5
Câu2:
X[SUP]2[/SUP]-2|x| -3=(|x|-1)[SUP]2[/SUP]-4=0
-->|x|-1=2 hoacj |x|-1=-2(tự giải em nhé)
Câu 3:2x[SUP]3[/SUP]-x[SUP]2[/SUP]+3x+6=0
2x[SUP]3[/SUP]+2x[SUP]2[/SUP]-3x[SUP]2[/SUP]-3x+6x+6=0
->2x[SUP]2[/SUP](x+1)-3x(x+1)+6(x+1)=O
->(x+1)(2x[SUP]2[/SUP]-3x+6)=0
->x=-1