bonsoir,
3 x² - 5 x = x ( 3 x - 5 )
x² - x = x ( x - 1 )
( 3 x + 2 )² - ( x - 10 )² = ( 3 x + 2 + x - 10 ) ( 3 x + 2 - x + 10) = ( 4 x - 8) ( 2 x + 12)
( 5 x + 4 )² - 36 = ( 5 x + 4 - 6 ) ( 5 x + 4 + 6 ) = ( 5 x - 2 ) ( 5 x + 10 )
( x + 1 )² - ( x - 1 )² = 4 x
( x + 1 + x - 1 ) ( x + 1 - x + 1 ) = 2 x ( 2) = 4 x
( 20 + 1 )² - ( 20 - 1 )² = ( 20 + 1 + 20 - 1 ) ( 20 + 1 - 20 + 1 ) = 40 * 2 = 80
21 ² - 19 ² = ( 20 + 1 )² - ( 20 - 1 )² = 80
51 ² - 49 ² = ( 50 + 1 )² - ( 50 - 1 )² = ( 50 + 1 + 50 - 1 ) ( 50 + 1 - 50 + 1 )
= 100 * 2 = 200
