Factoriser 4x②-20x+25 16-9y② 49-(3x+1)② (x+3)(x-9)-(x+3)②

Bonsoir , 
4x²-20x+25
= (2x)² - 2 × 2x × 5 + 5² 
= (2x+5)²  
16-9y²
= 4² - (3y)²
= (4-3y) (4+3y) 
49 - (3x+1)²
= 7² - (3x+1)²
= [ 7 -(3x+1) ] [ 7 + (3x+1) ] 
= [ 7 - 3x - 1 ] [ 7 + 3x + 1 ] 
= ( 6 - 3x ) ( 8 + 3x )  
(x+3)(x-9) - (x+3)²
= (x+3) [ ( x-9) - (x+3) ] 
= (x+3) [ x-9 - x - 3 ] 
= -12 (x+3)