(x+y)^2=36
x^2一y^2=(x+y)(x-y)=6(x-y)=24,x-y＝4
（x-y）∧2=16＝x^2-2xy+y^2
4xy=36-16＝20,xy=5
x^2+y^2=(x+y)^2-2xy=36-10=26