Đáp án:
Bài 1 :
a, ( 2x - 3y )( 2x + 3y )
= 4x² + 6xy - 6xy - 9y²
= 4x² - 9y²
b, ( 1 + 5a ).( 1 + 5a )
= 1 + 5a + 5a+ 25a²
= 1 + 10a + 25a²
c, ( x + 1 ).( x - 3 )
= x² - 3x + x - 3
= x² - 2x - 3
d, ( 2x - 1 )( 5x + 7 )
= 10x² + 14x - 5x - 7
= 10x² + 9x - 7
e, ( x - 2 ).( x² - 5x + 1 ) - x.( x + 11 )
= x³ - 5x² + x - 2x² + 10x² - 2 - x² - 11
= x³ + 2x² + x - 13
Bai 2 :
a, ( x + 1).( x + 3 ) - x( x + 2 ) = 7
x² + 3x + x + 3 - x² - 2x = 7
x + 3 = 7
x = 4
b, 2x.( 3x + 5 ) - x ( 6x - 1 ) = 33
6x² + 10x - 6x² + x = 33
11x = 33
x = 3
c, 1/4x² - ( 1/2x - 4 ).1/2x = -14
1/4x² - 1/4x² - 2x = -14
- 2x = -14
x = 7
Bài 3
a, A = ( 3x - 5 ).( 2x + 11 ) - ( 2x + 3 ).( 3x + 1 )
= 6x² + 33x - 10x - 55 - ( 6x² + 2x + 9x + 3 )
= 6x² + 33x - 10x - 55 - 6x² - 2x - 9x - 3
= 12x - 58
b, B = ( x - 5 ).( 2x + 3 ) - 2( x - 3 ) + x + 7
= 2x² + 3x - 10x - 15 - 2x + 6 + x + 7
= 2x² - 8x + 8