`a) (5x-2)(5x+2)-(5x+3)(5x-4)=8`
`<=>25x^2-4-25x^2+20x-15x+12=8`
`<=>(25x^2-25x^2)+(20x-15x)=8+4-12`
`<=>5x=0`
`<=>x=0`
Vậy `x=0`
`b)(4x-3)(4x+2)+(4x+5)(1-4x)=2.5^2`
`<=>16x^2+8x-12x-6+4x-16x^2+5-20x=50`
`<=>(16x^2-16x^2)+(8x-12x+4x-20x)=50+6-5`
`<=>-20x=51`
`<=>x=-51/20`
Vậy `x=-51/20`