解:∵x+y=10两边平方得:x²+2xy+y²=100∴x²+y²=100-2xy=100-2×5=90
(x+y)^2=x^2+2xy+y^2=x^2+y^2+10=100 x^2+y^2=90
x²+y²=(x+y)²-2xy=10²-2×5=90
x^2+y^2=(x+y)^2-2xy=10^2-2*5=90
90