Đáp án:
`a)x=1`
`b)x=1`
`c)x∈{2/5;3/2}`
Giải thích các bước giải:
`a)(5x+1)²-(5x-3)(5x+3)=20`
`⇔25x²+10x+1-[(5x)²-3²]=20`
`⇔25x²+10x+1-(25x²-9)=20`
`⇔25x²+10x+1-25x²+9=20`
`⇔(25x²-25x²)+10x+(1+9)=20`
`⇔10x+10=20`
`⇔10x=20-10`
`⇔10x=10`
`⇔x=10:10`
`⇔x=1`
Vậy `x=1`
`b)(2x+3)²-(2x+1)(2x-1)=22`
`⇔4x²+12x+9-[(2x)²-1²]=22`
`⇔4x²+12x+9-(4x²-1)=22`
`⇔4x²+12x+9-4x²+1=22`
`⇔(4x²-4x²)+12x+(9+1)=22`
`⇔12x+10=22`
`⇔12x=22-10`
`⇔12x=12`
`⇔x=12:12`
`⇔x=1`
Vậy `x=1`
`c)(5x-2)²+(2-5x)(3x+1)=0`
`⇔(2-5x)²+(2-5x)(3x+1)=0`
`⇔(2-5x)(2-5x+3x+1)=0`
`⇔(2-5x)(3-2x)=0`
`⇔`$\left[\begin{matrix} 2-5x=0\\ 3-2x=0\end{matrix}\right.$
`⇔`$\left[\begin{matrix} 5x=2\\ 2x=3\end{matrix}\right.$
`⇔`$\left[\begin{matrix} x=\dfrac{2}{5}\\ x=\dfrac{3}{2}\end{matrix}\right.$
Vậy `x∈{2/5;3/2}`
