bài 4:
P(x)= x³-2x+7-x
= x³+(-2x-x)+7
= x³-3x+7
Q(x)= -x³+2x-3+2x-x³-3
= (-x³-x³)+(2x+2x)+(-3-3)
= -2x³+2x-6
M(x)= (x³-3x+7)+(-2x³+2x-6)
= x³-3x+7-2x³+2x-6
= (x³-2x³)+(-3x+2x)+(7-6)
= -1x³-1x+1
N(x)=(x³-3x+7)-(-2x³+2x-6)
= x³-3x+7-2x³-2x+6
= (x³+2x³)+(-3x-2x)+(7+6)
=3x³-5x+12
bài 5:
P(x)=5x³+$2x^{4}$-$x^{2}$+$3x^{2}$-$x^{3}$-$2x^{4}$+1-$4x^{3}$
=(5$x^{3}$-$x^{3}$-$x4^{3}$)+($2x^{4}$-$2x^{4}$ )+(-$x^{2}$ +$3x^{2}$)+1
=$2x^{2}$+1
P(1)=2.1²+1 P(-1)=2.-1²+1
=2 = 3
