解(x+y)²+10(x+y)+25=(x+y)²+2×5×(x+y)+5²——将x+y看成整体=[(x+y)+5]²=(x+y+5)²(x+2)(x+n)=x²+nx+2x+2n=x²+(n+2)x+2n=x²+kx-12∴2n=-12,n+2=k∴n=-6,k=-44a²+12a+...