`#Sad`
`a)`
`(2x+2)(4x^2-4x+4)-2x(4x^2-2) = 15`
`⇔ 8x^3+8-8x^3+4x-15 = 0`
`⇔ 4x-7 = 0`
`⇔ 4x = 7`
`⇔ x = 7/4`
`\text{Vậy S=}` `{7/4}`
`b)`
`2x(2x-5)(2x+5)-(2x+2)(4x^2-4x+4) = 3`
`⇔ 2x(4x^2-25)-8x^3-8-3 = 0`
`⇔ 8x^3-50x-8x^3-11 = 0`
`⇔ -50x = 11`
`⇔ x = -(11)/(50)`
`\text{Vậy S=}` `{-(11)/(50)}`