a) (3x²-2x+1)-(-x²+4x-5)=3x²-2x+1+x²-4x+5=4x²-6x+6=2(2x²-3x+3)
b) (4x³-12x²+5x-7)-(3x³-8x²-2x-4)=4x³-12x²+5x-7-3x³+8x²+2x+4=x³-4x²+7x-3
c) 20x²-(-5x²+4x-18)-(6-3x)-(2x²+6x-11)= 20x²+5x²-4x+18-6+3x-2x²-6x+11=23x²-7x+23
d)7x(-3x+2y)-5x+(10x-2y)=7x-3x+2y-5x+10x-2y=7x-3x-5x+10x=9x
e) (-4a+3b-10c)-(11-2a-4b)+(6a+14c-20b)=-4a+3b-10c-11+2a+4b+6a+14c-20b=4a-13b+4c-11
f) (m+n+p)-(m-n-p)+(-m-n+p)-3p=m+n+p-(m-n-p)-m-n+p-3p=+p-m+n+p+p-3p=-m+n
