Question

求值（x^2+xy)/(x^2-2xy-3y^2)*(3y-x)/(x-y)+(x^-1+y^-1)÷(x^-1-y^-

Answer 1

原式=[x(x+y)/(x-3y)(x+y)][-(x-3y)/(x-y)]+(1/x+1/y)/(1/x-1/y)

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

=(2x+y)/(y-x)

=3/(-3)

=-1