a. Thể tích hình hộp chữ nhất là: \(�.(�+1)(�−1)=�.(�2−1)=�3−�x.(x+1)(x−1)=x.(x2−1)=x3−x\)

b. Thể tích của hình hộp chữ nhật tại x = 4 là:

\(43−4=6043−4=60\)

\(2x 4 −3�3−3x 3 −3�2−3x 2 +6�+6x −2−2 �2−2x 2 −2 2�42x 4 −4�2−4x 2 2�2−3�+12x 2 −3x+1 −− −3�3−3x 3 +�2+x 2 +6�+6x −2−2 −3�3−3x 3 +6�+6x −− �2x 2 −2−2 �2x 2 −2−2 −− 2�42x 4 −3�3−3x 3 −3�2−3x 2 +6�+6x −2−2 �2−2x 2 −2 2�42x 4 −4�2−4x 2 2�2−3�+12x 2 −3x+1 −− −3�3−3x 3 +�2+x 2 +6�+6x −2−2 −3�3−3\)

5x(4x2−2x+1)−2x(10x2−5x+2)=−36 

5�.4�2+5�.(−2�)+5�.1+(−2�).10�2+(−2�).(−5�)+(−2�).2=−365x.4x2+5x.(−2x)+5x.1+(−2x).10x2+(−2x).(−5x)+(−2x).2=−36 

20�3+(−10�2)+5�+(−20�3)+10�2+(−4�)=−3620x3+(−10x2)+5x+(−20x3)+10x2+(−4x)=−36

(20�3−20�3)+(−10�2+10�2)+(5�−4�)=−36(20x3−20x3)+(−10x2+10x2)+(5x−4x)=−36

�=−36x=−3

a) Tổng của \(P\)\(\left(x\right)+Q\left(x\right)\) là:

\(P\left(x\right)+Q\left(x\right)\)=\(�4−5�3+4�−5−�4+3�2+2�+1x4−5x3+4x−5−x4+3x2+2x+1\)

\(=−5�3+3�2+6�−4=−5x3+3x2+6x−4\)

b. \(�(�)=�4−5�3+4�−5−(−�4+3�2+2�+1)R(x)=x4−5x3+4x−5−(−x4+3x2+2x+1)\)

\(=�4−5�3+4�−5+�4−3�2−2�−1=x4−5x3+4x−5+x4−3x2−2x−1\)

\(=2�4−5�3−3�2+2�−6=2x4−5x3−3x2+2x−6\)