$\large{\color{red}{\textbf{Giải:}}}$

`bb{a))`

`(5x - 2)^2 - 25x(x - 3) + 4`

`= 25x^2 - 20x + 4 - 25x^2 + 75x + 4`

`= (25x^2 - 25x^2) + (-20x + 75x) + (4 + 4)`

`= 55x + 8` 

`bb{b))` `(6x - 2)(6x + 2) - (6x + 1)^2`

`= (6x)^2 - (2)^2 - [(6x)^2 + 2*6x*1 + 1^2]`

`= 36x^2 - 4 - (36x^2 + 12x + 1)`

`= 36x^2 - 4 - 36x^2 - 12x - 1`

`= (36x^2 - 36x^2) - 12x - 5`

`= -12x - 5`

`bb{c))` `(3x + 5)^2 - (3x + 4)(3x - 4)`

`= 9x^2 + 30x + 25 - (9x^2 - 16)`

`= 9x^2 + 30x + 25 - 9x^2 + 16`

`= (9x^2 - 9x^2) + 30x + 41`

`= 30x + 41`

`bb{d))` `(4x - 1)(4x + 1) - (4x + 5)^2`

`= (4x)^2 - 1^2 - [(4x)^2 + 2*4x*5 + 25]`

`= 16x^2 - 1 - (16x^2 + 40x + 25)`

`= 16x^2 - 1 - 16x^2 - 40x - 25`

`= (16x^2 - 16x^2) - 40x - 26`

`= -40x - 26`