(y-2)(y的2次幂-6y-9)-y(y的2次幂-2y-15),其中y=-2
=y^3-6y^2-9y-2y^2+12y+18-y^3+2y^2+15y
=-6y^2+18y+18
=-6*(-2)^2+18*(-2)+18
=-24-36+18
=-42