d, ax^2+a^2y-7x-7y e, ax^2+ay-bx^2-by f, x(x+1)^2+x(x-5)-5(x+1)^2

`a)` Sửa đề : `a^2x + a^2y - 7x - 7y`

`ax^2 + a^2y - 7x - 7y`

` = (a^2x - 7x) + (a^2y -7y)`

` = x . (a^2 - 7) + y. (a^2  -7)`

` = (x+y) . (a^2 -7)`

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`b)`

`ax^2 + ay - bx^2 - by`

` = (ax^2 + ay) - (bx^2 + by)`

`= a . (x^2 + y) - b . (x^2 + y)`

` = (a-b) . (x^2 + y)`

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`c)`

`x . (x+1)^2 + x . (x-5) - 5 . (x+1)^2`

` = [ x . (x+1)^2 - 5 . (x+1)^2 ] + x . (x-5)`

` = (x-5) . (x+1)^2 + x . (x-5)`

` = (x-5) . [ (x+1)^2 + x]`

` = (x-5). (x^2 + 2x + 1 + x)`

` = (x-5) . (x^2 + 3x+1)`