Question

已知x^2+xy=12,xy+y^2=15,求(x+y)^2及（x+y)（x-y)的值

Answer 1

x^2+xy=12,

xy+y^2=15,

x^2+xy+xy+y^2=12+15

(x+y)^2=27

x^2+xy=12,

xy+y^2=15

x^2-y^2=-3

（x+y)（x-y)=-3