Question

Bài 3. Thu gọn các biểu thức sau:

a) x(x + 1) – 2x(x – 2)

b) -3x( x – 1) + (x – 1)(x + 1)

c) (3x – 2)(3x + 2) – (x – 1)(x + 2)

Answer 1

a) x(x + 1) - 2x(x - 2) = x² + x - 2x² + 4x = -x² + 5x

b) -3x(x - 1) + (x - 1)(x + 1) = -3x² + 3x + x² - 1 = -2x² + 3x  - 1

c) (3x - 2)(3x + 2) - (x - 1)(x + 2) = 9x² - 4 - x² - x + 2 

= 8x² - x - 2

Answer 2

a, x(x+1) - 2x(x -2 )

= x² +x  - 2x² + 4x  = -x² + 5x

b, -3x( x - 1 ) + ( x -1 ) ( x+1 )

= -3x² + 3x + x² -1

= -2x² + 3x -1

c, ( 3x-2 ) ( 3x + 2 ) - ( x -1 ) ( x +2 )

= 9x² - 4 - ( x² + 2x -x -2 ) 

= 9x² -4 - x² -2x + x + 2

= 8x² -x -2

*Sxl

Answer 3

Trả lời:

a) x ( x + 1 ) - 2x ( x - 2 ) = x² + x - 2x² + 4x = - x² + 5x

b) - 3x ( x - 1 ) + ( x - 1 ) ( x + 1 ) = - 3x² + 3x + x² - 1 = - 2x² + 3x - 1

c) ( 3x - 2 ) ( 3x + 2 ) - ( x - 1 ) ( x + 2 ) = 9x² - 4 - ( x² + 2x - x - 2 ) = 9x² - 4 - x² - 2x + x + 2 = 8x² - x - 2