Đáp án:
`A_5=(x²-2x+6)/(2x)`
Giải thích các bước giải:
`A_5=(x²+2x)/(2x+12)+(x-6)/x+(108-6x)/[2x(x+6)]`
`=(x²+2x)/[2(x+6)]+(x-6)/x+(108-6x)/[2x(x+6)]`
`=[x(x²+2x)]/[2x(x+6)]+[2(x-6)(x+6)]/[2x(x+6)]+(108-6x)/[2x(x+6)]`
`=[x(x²+2x)+2(x-6)(x+6)+108-6x]/[2x(x+6)]`
`=(x³+2x²+2(x²-36)+108-6x)/[2x(x+6)]`
`=(x³+2x²+2x²-72+108-6x)/[2x(x+6)]`
`=[x³+(2x²+2x²)-6x+(-72+108)]/[2x(x+6)]`
`=(x³+4x²-6x+36)/[2x(x+6)]`
`=(x³+6x²-2x²+6x-12x+36)/[2x(x+6)]`
`=[(x³+6x²)-(2x²+12x)+(6x+36)]/[2x(x+6)]`
`=[x²(x+6)-2x(x+6)+6(x+6)]/[2x(x+6)]`
`=[(x+6)(x²-2x+6)]/[2x(x+6)]`
`=(x²-2x+6)/(2x)`
