Đáp án:
`a)x=-39/20`
`b)x=-33/20`
Giải thích các bước giải:
`a)(x-5)(x+5)-(x+3)²+3(x-2)²=(x+1)²-(x+4)(x-4)+3x²`
`⇔x²-25-(x²+6x+9)+3(x²-4x+4)=x²+2x+1-(x²-16)+3x²`
`⇔x²-25-x²-6x-9+3x²-12x+12=x²+2x+1-x²+16+3x²`
`⇔(x²-x²+3x²)-(6x+12x)+(-25-9+12)=(x²-x²+3x²)+2x+(1+16)`
`⇔3x²-18x-22=3x²+2x+17`
`⇔3x²-18x-3x²-2x=17+22`
`⇔-20x=39`
`⇔x=-39/20`
Vậy `x=-39/20`
`b)(2x+3)²+(x-1)(x+1)=5(x+2)²-(x-5)(x+1)+(x+4)²`
`⇔4x²+12x+9+x²-1=5(x²+4x+4)-(x²+x-5x-5)+x²+8x+16`
`⇔(4x²+x²)+12x+(9-1)=5x²+20x+20-x²-x+5x+5+x²+8x+16`
`⇔5x²+12x+8=(5x²-x²+x²)+(20x-x+5x+8x)+(20+5+16)`
`⇔5x²+12x+8=5x²+32x+41`
`⇔5x²+12x-5x²-32x=41-8`
`⇔-20x=33`
`⇔x=-33/20`
Vậy `x=-33/20`
