Đáp án:
`a)x=-2`
`b)x=-20`
`c)x=-5`
Giải thích các bước giải:
`a)(2x+1)²-4(x+2)²=9`
`⇔4x²+4x+1-4(x²+4x+4)=9`
`⇔4x²+4x+1-4x²-16x-16=9`
`⇔(4x²-4x²)+(4x-16x)+(1-16)=9`
`⇔-12x-15=9`
`⇔-12x=9+15`
`⇔-12x=24`
`⇔x=24:(-12)`
`⇔x=-2`
Vậy `x=-2`
`b)(x+3)²-(x-4)(x+8)=1`
`⇔x²+6x+9-(x²+8x-4x-32)=1`
`⇔x²+6x+9-x²-8x+4x+32=1`
`⇔(x²-x²)+(6x-8x+4x)+(9+32)=1`
`⇔2x+41=1`
`⇔2x=1-41`
`⇔2x=-40`
`⇔x=(-40):2`
`⇔x=-20`
Vậy `x=-20`
`c)3(x+2)²+(2x-1)²-7(x+3)(x-3)=36`
`⇔3(x²+4x+4)+4x²-4x+1-7(x²-9)=36`
`⇔3x²+12x+12+4x²-4x+1-7x²+63=36`
`⇔(3x²+4x²-7x²)+(12x-4x)+(12+1+63)=36`
`⇔8x+76=36`
`⇔8x=36-76`
`⇔8x=-40`
`⇔x=(-40):8`
`⇔x=-5`
Vậy `x=-5`
