Đáp án:
`1.`
`a)25x²y²-16a²`
`b)a³-a²b-4ab²+4b³`
`2.`
`x=-20/13`
Giải thích các bước giải:
`1.`
`a)(5xy-4a)(5xy+4a)`
`=(5xy)²-(4a)²`
`=25x²y²-16a²`
`b)(a-2b)(a+2b)(a-b)`
`=[a²-(2b)²](a-b)`
`=(a²-4b²)(a-b)`
`=a³-a²b-4ab²+4b³`
`2.`
`(5x-3)(6x-1)-10x(3x-1)=23`
`⇔30x²-5x-18x+3-30x²+10x=23`
`⇔(30x²-30x²)+(-5x-18x+10x)+3=23`
`⇔-13x+3=23`
`⇔-13x=23-3`
`⇔-13x=20`
`⇔x=-20/13`
Vậy `x=-20/13`