Question

已知(x+y)^2=18,(x-y)^2=6求x^2+y^2和xy的值

Answer 1

(x+y)^2=18---->(x^2+y^2)+2xy=18.(1)

,(x-y)^2=6---->(x^2+y^2)-2xy=6.(2)

(1)+(2):2(x^2+y^2)=24

x^2+y^2=12

(1)-(2):4xy=12

xy=3