a)(m+n)(m-2)+(m-n)(m+1)=m²-2m+nm-2n+m²+m-nm-n= 2m²-m-3n
b) (3x-2)(3x-2y+1)-4x(2x-3y+1)=9x²-6xy+3x-6x+4y-2-8x²+12xy-4x=x²+6xy-7x+4y-2
c) 3(m+1)(n-2)+2(n+1)(m-2)=3mn-6m+3n-6+2nm-4n+2m-4=5mn-4m-n-10
d) x(x+1)(x+2)-x(-1)(x-2)=x(x²+2x+x+2)-x(-x+2)=x³+2x²+x²+2x+x²-2x= x³+4x²