x-y=9,x*y=5x^2+y^2=(x-y)^2+2xy=81+10=91(x+y)^2=(x-y)^2+4xy=81+20=101
x*x+y*y=(x-y)*(x-y)+2xy(x+y)(x+y)=x*x+2xy+y*y 其x*x+y*y第一步已经求出了带入就行
x^2+y^2=(x-y)^2+2xy=81+10=91(x+y)^2=(x-y)^2+4xy=81+20=101
