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16 x² + 48 x +36 = ( 4 x + 6 )²

64 - 25 x² = ( 8 - 5 x ) ( 8 + 5 x )

49 x² - 28 x + 4 = ( 7 x - 2 )²

9 x² - 25 + ( 3 x - 5 ) ( 2 x + 15 )

= ( 3 x - 5 ) ( 3 x + 5 ) + ( 3 x - 5 ) ( 2 x +15 )

= ' 3 x - 5 ) ( 3 x + 5 + 2 x + 15 )

= ( 3 x - 5 ) ( 5 x + 20 )

= 5 ( 3 x - 5 ) ( x + 4 )