已知x+y=8 (x-y)的平方=4 x的平方+y的平方的值?

x+y=8 (x+y)2 =x2+2xy+y2
(x-y)的平方=4 (x-y)2=x2-2xy+y2

则有x2+y2 =(x+y)2 +(x-y)2 /2
=64+4 /2
=34

x+y=8
（x+y）^2=8^2=64
x^2+2xy+y^2=64----(1)
(x-y)^2=4
x^2-2xy+y^2=4-----(2)
(1)+(2)
2(x^2+y^2)=68
x^2+y^2=34

破问题有歧义

34

40