(x-y)^2=252xy=2求出x^2+y^2=27
x-y=5两边平方得x的2次方+y的2次方-2xy=25所以x的2次方+y的2次方=27
因为:(x-y)^2=x^2-2xy+y^2所以:x^2+y^2=(x-y)^2+2xy所以:x^2+y^2=5^2+2*1 =25+2 =27