Question

解方程组：x+y=xy=11 (1) x*x*y+x*y*y=30 (2)

Answer 1

1.xy-x-y=0

xy-x-y+1=0

(x-1)(y-1)=0

so,x=1or y=1代入上式

得x=1 y=10

x=10 y=1

2.xy(x+y)=30

30=2*3*5

则x,y,x+y分别为2,3,5

凑之

x=2 y=3

x=3 y=2