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( 6 x + 1 ) ( x - 2 ) = 6 x² - 12 x + x - 2 = 6 x² - 11 x - 2

( 10 x + 3 )²  = 100 x² + 60 x + 9

( 3 x + 1 ) ( x - 5 ) + 7 ( 3 x + 1 )

= ( 3 x + 1 ) ( x - 5 + 7 )

= ( 3 x + 1 ) ( x + 2 )

25 x² - 40 x + 16 = ( 5 x - 4 )²

( x + 2 )² -  9

=  x² + 4 x + 4 - 9

=  x² + 4 x -  5

( x + 2 )² - 9

= ( x + 2 - 3 ) ( x + 2 + 3)

= ( x - 1 ) ( x + 5 )