Question

已知x=1/2 y=1/3 z=1/4 则(xx+yy-zz+2xy)/(xx-yy+zz-2xz) 得多少?

Answer 1

x2+y2-z2+2xy/x2-y2+z2-2xz

=(x+y)2-z2/(x-z)2-y2

=(x+y-z)(x+y+z)/(x-y-z)(x-z+y)

=(x+y+z)/(x-y-z)

然后就是代入了