Đáp án:
a) x³ - 8x² + 18x + 21
b) 3x³ - x² + 6x - 6
c) x² + 7x + 12
d) - 2x + 8
e) 5x - 5
f) - 5x - 1
Giải thích các bước giải:
a) -5x( x - 5) + ( x - 3)(x² - 7)
= - 5x² + 25x + x³ - 3x² - 7x + 21
= x³ - 8x² + 18x + 21
b) 4x( x² - x +1) + ( x² - 2)( - x +3)
= 4x³ - 4x² + 4x - x³ + 3x² + 2x - 6
= 3x³ - x² + 6x - 6
c) (- x + 5)(x + 3) + ( 2x -1)(x + 3)
= -x² - 3x + 5x + 15 + 2x² + 6x - x -3
= x² + 7x + 12
d) (x -1)(x + 2) - ( x + 5)(x - 2)
= x² - x + 2x - 2 - x² - 5x + 2x + 10
= -2x + 8
e) (2x - 5)( 3x + 1) - 6x( x - 3)
= 6x² + 2x - 15x - 5 - 6x² + 18x
= 5x - 5
f) (x - 1)(x² + x + 1) - x( x² + 5)
= x³ - 1 - x³ - 5x
= - 5x - 1
