Question

已知(x y)^2=10,(x-y)^2=6.求2xy与x^2+y^2的值

Answer 1

(x y)^2=10 得出x y=正负根号10 2xy=正负2*根号10

(x-y)^2=X^2+y^2-2xy=6 X^2+y^2=6+2xy 因为2*根号10>6 而 X^2+y^2>0

所以2xy=2*根号10 X^2+y^2=6+2*根号10