`6a^4 + 7a^3 - 37a^2 - 8a + 12`

`= ( 6a^4 + 19a^3 + a^2 - 6a ) - ( 12a^3 + 38a^2 - 2a + 12 )`

`= a ( 6a^3 + 19a^2 + a - 6 ) - 2 ( 6a^3 + 19a^2 - a - 6 )`

`= ( a - 2 ) ( 6a^3 + 19a^2 - a - 6 )`

`= ( a - 2 ) [ ( 6a^3 + 18a^2 ) + ( a^2+ 3a ) - ( 2a + 6 )]`

`= ( a - 2 ) [ ( 6a^2 ( a + 3 ) + a ( a + 3 ) - 2 ( a + 3 ) ]`

`= ( a - 2 ) ( a + 3 ) ( 6a^2 + a - 2 )`

`= ( a - 2 )( a + 3 ) ( 6a^2- 3a + 4a - 2 )`

`= ( a - 2 )( a + 3 ) [ 3a ( 2a - 1 ) + 2 ( 2a - 1 )]`

`= ( a - 2 ) ( a + 3 ) ( 3a + 2 ) ( 2a - 1 )`