a, 400 - x²
= 20² - x²
= ( 20 - x )( 20 + x ).
b, 125 + x³
= 5³ + x³
= ( 5 + x )( 5² - 5x + x² )
= ( 5 + x )( 25 - 5x + x² ).
c, 1000 - a³
= 10³ - a³
=( 10 - a )( 10² + 10a + a² )
= ( 10 - a )( 100 + 10a + a² ).
d, 4x² - 9
= ( 2x )² - 3²
= ( 2x - 3 )( 2x + 3 ).
e, 3x²( 2x - 4 ) - x( 2x - 4 )
= ( 2x - 4 )( 3x² - x )
= 2( x - 2 ). x( 3x - 1)
f, ( x - 7 )² - ( 2x - 5 )²
= ( x - 7 - 2x + 5 )( x - 7 + 2x - 5 )
= ( -x - 2 )( 3x - 12 )
g, 2ax + 14x - 3a - 21
= ( 2ax + 14x ) - ( 3a + 21 )
= 2x( a + 7 ) - 3( a+ 7 )
= ( a + 7 )( 2x - 3 )
h, 5x - ax - 25 + 5a
= ( 5x - ax ) - ( 25 - 5a )
= x( 5 - a ) - 5( 5 - a )
= ( 5 - a )( x - 5 )
i, a² - 4a + 4 - b²
= ( a² - 4a + 4 ) - b²
= ( a - 2 )² - b²
= ( a - 2 - b )( a - 2 + b )
k, 5a( a - 8b ) + ( a - 8b )²
= 5a( a - 8b ) + ( a - 8b )( a - 8b )
= ( a - 8b )( 5a + a - 8b )
_Chúc pẹn học tốt nghen_
