a) ab ( a-b ) + bc ( b-c ) + ca( c-a )
= a²b - ab² + b²c - bc² + ca ( c-a )
= a² ( a²b - bc² ) - ( ab² - b²c ) + ca ( c-a )
= b ( a²- c² ) - b² ( a-c ) - ca ( a- c )
= b ( a- c ) ( a+c) - b² ( a-c) - ca ( a-c )
= ( a-c ) ( ba + bc - b² - ca )
= ( a-c ) [ a ( b-c ) + b ( c-b) ]
= ( a-c ) ( b - c ) ( a - b )
b ) ( a + b + c )³ - a³ - b³ - c³
= [ a + ( b+c) ]³ - a³ - b³ - c³
= a³+3a²(b+c) + 3a ( b+c)² + (b+c)³ - a³-b³ - c³
= 3a² ( b + c ) + 3a ( b+c)² + b³ + 3b²c + 3bc² + c³ - b³ - c³
= 3a² ( b+c) + 3a ( b+c ) + bc ( b+c)
= ( b + c ) ( 3a² + 3a + 3bc )
= 3 ( b+c ) ( a² + a + bc )
c ) 4a²b²- ( a²-b²-c²)
= ( 2ab ) ² - ( a²+b²- c²)
= ( 2ab - a² - b² + c² ) ( 2ab + a² + b² - c² )
= [ - ( a² + b² - 2ab ) + c² ] [ ( a + b ) ² - c²]
= [ c²- ( a - b ) ² ] [ ( a + b ) ² - c² ]
= ( c- a+ b) ( c + a - b ) ( a + b - c )( a + b + c )
Có gì k hiểu hỏi mk nhé :)
Cho mk ctlhn nha ***
