Question

Tính:

a) (x - 3).(x² + 3x + 9) - (x³ + 3)

=

b) (x - 1).(x² + x + 1) - (x + 1).(x - 1)

=

c) 2.(x - 1)² - 2.(x +3).(x - 3)

=

Answer 1

Tính:

a) Ta có: \(\left(x-3\right)\left(x^2+3x+9\right)-\left(x^3+3\right)\)

\(=x^3-3^3-x^3-3=-6\)

b) Ta có: \(\left(x-1\right)\left(x^2+x+1\right)-\left(x+1\right)\left(x-1\right)\)

\(=\left(x-1\right)\left[\left(x^2+x+1\right)-\left(x+1\right)\right]\)

\(=\left(x-1\right)\left(x^2+x+1-x-1\right)\)

\(=\left(x-1\right)x^2\)

\(=x^3-x^2\)

c) Ta có: \(2\left(x-1\right)^2-2\left(x+3\right)\left(x-3\right)\)

\(=2\left(x^2-2x+1\right)-2\left(x^2-3^2\right)\)

\(=2\left[\left(x^2-2x+1\right)-\left(x^2-9\right)\right]\)

\(=2\left(x^2-2x+1-x^2+9\right)\)

\(=2\left(-2x+10\right)\)

\(=-4x+20\)

Answer 2

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