Bài 5:
`a)5x(1/5x-2)+3(6-1/3x²)=12`
`⇔x²-10x+18-x²=12`
`⇔(x²-x²)-10x+18=12`
`⇔-10x+18=12`
`⇔-10x=12-18`
`⇔-10x=-6`
`⇔x=6/10`
`⇔x=3/5`
Vậy `x=3/5`
`b)7x(x-2)-5(x-1)=7x²+3`
`⇔7x²-14x-5x+5=7x²+3`
`⇔7x²-19x+5=7x²+3`
`⇔7x²-19x-7x²=3-5`
`⇔-19x=-2`
`⇔x=2/19`
Vậy `x=2/19`
`c)2(5x-8)-3(4x-5)=4(3x-4)+11`
`⇔10x-16-12x+15=12x-16+11`
`⇔(10x-12x)+(-16+15)=12x+(-16+11)`
`⇔-2x-1=12x-5`
`⇔-2x-12x=-5+1`
`⇔-14x=-4`
`⇔x=4/14`
`⇔x=2/7`
Vậy `x=2/7`
`d)5x-3{4x-2[4x-3(5x-2)]}=182`
`⇔5x-3{4x-2[4x-15x+6]}=182`
`⇔5x-3{4x-2[-11x+6]}=182`
`⇔5x-3{4x+22x-12}=182`
`⇔5x-3{26x-12}=182`
`⇔5x-78x+36=182`
`⇔-73x+36=182`
`⇔-73x=182-36`
`⇔-73x=146`
`⇔x=146:(-73)`
`⇔x=-2`
Vậy `x=-2`
Bài 6:
`a)VT=a(b-c)-b(a+c)+c(a-b)`
`=ab-ac-ab-bc+ac-bc`
`=(ab-ab)+(-ac+ac)-(bc+bc)`
`=-2bc`
`=VP`
`⇒đpcm`
`b)VT=a(1-b)+a(a²-1)`
`=a-ab+a³-a`
`=(a-a)+(a³-ab)`
`=a(a²-b)`
`=VP`
`⇒đpcm`
