Question

若xy=b,且x2分之1+y2分之1=a则 《x+y》2=?

Answer 1

1/x^2+1/y^2

=(x^2+y^2)/x^2y^2=a

x^2+y^2=ab^2

(x+y)^2-2xy=ab^2

(x+y)^2=ab^2+2