Question

x+y=根号下5倍根号3-3倍根号5 x-y=根号下5倍根号3+3倍根号5,则xy的值为?

Answer 1

(x+y)²-(x-y)²=(5√3-3√5)-(5√3+3√5)

x²+2xy+y²-x²+2xy+y²=-6√5

4xy=-6√5

xy=-3√5/2