Question

Rút gọn biểu thức:

b) (x - 3)(x² +3x +9) - x(x² - 9)

c) (x + 5)(x - 5) - (x - 3)(x + 2)

Answer 1

Answer 2

\(b,\left(x-3\right).\left(x^2+3x+9\right)-x.\left(x^2-9\right)\)

\(=x^3+3x^2+9x-3x^2-9x-27-x^3+9x\)

\(=\left(x^3-x^3\right)+\left(3x^2-3x^2\right)+\left(9x+9x\right)-27\)

\(=18x-27\)

c,\(\left(x+5\right).\left(x-5\right)-\left(x-3\right).\left(x+2\right)\)

\(=x^2-5^2-x^2-2x+3x+6\)

\(=x-19\)

Answer 3

b) x³ - 27 - x³ + 9x

= 9x - 27

= 9(x - 3)

c) x² - 25 - (x² + 2x - 3x - 6)

= x² - 25 - x² - 2x + 3x + 6

= -x² - x - 19