a)Đa thứcA(x)

A(x)=−4x5−x3+4x2+5x+9+4x5−6x2−2

=(−4x5+4x5)−x3+(4x2−6x2)+5x+(9−2)

=−x3−2x2+5x+7

Đa thức B(x)B(x)

B(x)=−3x4−2x3+10x2−8x+5x3−7−2x3+8x

=−3x4+(−2x3+5x3−2x3)+10x2+(−8x+8x)−7

=−3x4+x3+10x2−7

b)

A(x)+B(x)

=(−x3−2x2+5x+7)+(−3x4+x3+10x2−7)

=−x3−2x2+5x+7−3x4+x3+10x2−7

=−3x4+(−x3+x3)+(−2x2+10x2)+5x+(7−7)

A(x)−B(x)

=(−x3−2x2+5x+7)−(−3x4+x3+10x2−7)

=−x3−2x2+5x+7+3x4−x3−10x2+7

=3x4+(−x3−x3)+(−2x2−10x2)+5x+(7+7)

=3x4−2x3−12x2+5x+14

c)

Ta có:

P(x)=−3x4+8x2+5x

P(−1)=(−3).(−1)4+8.(−1)2+5.(−1)

=(−3)+8−5

=0
phần c ko rõ đầu bài