Question

已知x+y=-5,x*x+y*y=19求xy和（x-y)*(x-y)的ŀ

Answer 1

xy={（x+y）（x+y）-（x*x+y*y）}/2=3
（x-y)*(x-y)=x*x+y*y-2xy=13

Answer 2

xy=[(x+y)(x+y)-(x²+y²)]/2
=3
（x-y)(x-y)
=x²+y²-2xy
=13