Bonjour, je n'arrive pas à factoriser ces expression: 7x²-28=? (2x-3)²-(5x+2)²=? (x-5)²-2(x-5)(x-3)=?

7x^2-28=7x^2-7*4=7*(x^2-4)=7*(x^2-2^2)=7*((x+2)(x-2)) (x-5)^2-2(x-5)(x-3)=(x-5)(x-5)-2*(x-5)(x-3)=(x-5)(x-5-2(x-3))=(x-5)(x-5-2x+6) =(x-5)(-x+1)

7X^2 - 28 =
7x^2 - 4 * 7 =
7 (x^2 - 4)

(2x -3)^2 -(5x+2)^2 =
a^2 - b^2 = (a+b) (a-b)
(2x-3 + 5x + 2) ( 2x - 3 - ( 5x + 2 ) )=
(7x - 1) ( -3x - 5)=

(x- 5) ^2 - 2 ( x-5) ( x + 3)=
(x-5) (x-5) -2 ( x-5) (x + 3) =
(x-5) ((x-5) - (2(x-5) (x + 3) =
(x-5) ( x - 5 - ( (2x -10) ( x+3)=
(x-5) ( x-5 - ( 2x^2 + 6x - ( 10x + 30) )=
(x-5) ( x- 5 - (2x^2 + 6x - 10x - 30)=
(x-5) (x-5 - ( 2x^2 - 4x - 30) =
(x-5) (x-5 - 2x^2+ 4x + 30)=
(x-5) (-2x^2+5x+25)