长x
宽y
x-5=y+2
x=y+7
xy=(x-5)(y+2)
y(y+7)=[(y+7)-5](y+2)
yy+7y=(y+2)(y+2)
yy+7y=yy+2y+2y+4
7y=2y+2y+4
7y=4y+4
3y=4
y=1.3(循环3)
x=8.3(循环3)