解：<1>x²+y² =(x-y)^2+2xy=5^2+2*2=29<2>（x+y）²=(x-y)^2+4xy=5^2+4*2=33
(x-y)^2+2xy=x^2+y^2=25+4=29(x-y)^2+4xy=(x+y)^2=25+8=33
(1)x^2+y^2=(x+y)^2-2xy=21(x-y)^2=(x+y)^2-4xy=17
x²+y² =25+2X2=29(x+y）²=29-2X2=25
