`10.`
`P=(m²-2m+4)(m+2)-m³+(m+3)(m-3)-m²-18`
`=m³+2m²-2m²-4m+4m+8-m³+m²-9-m²-18`
`=(m³-m³)+(2m²-2m²+m²-m²)+(-4m+4m)+(8-9-18)`
`=-19`
Vậy giá trị của `P` không phụ thuộc vào `m`
`11.`
`a)(x²+2x+4)(2-x)+x(x-3)(x+4)-x²+24=0`
`⇔8-x³+(x²-3x)(x+4)-x²+24=0`
`⇔8-x³+x³+4x²-3x²-12x-x²+24=0`
`⇔(-x³+x³)+(4x²-3x²-x²)-12x+(8+24)=0`
`⇔-12x+32=0`
`⇔-12x=-32`
`⇔x=32/12`
`⇔x=8/3`
Vậy `x=8/3`
`b)(x/2+3)(5-6x)+(12x-2)(x/4+3)=0`
`⇔5/2x-3x²+15-18x+3x²+36x-1/2x-6=0`
`⇔(-3x²+3x²)+(5/2x-18x+36x-1/2x)+(15-6)=0`
`⇔20x+9=0`
`⇔20x=-9`
`⇔x=-9/20`
Vậy `x=-9/20`
`12.`
`VT=(x^4-x³y+x²y²-xy³+y^4)(x+y)`
`=x^5-x³y²+x³y²+x²y³-x²y³-xy^4+xy^4+y^5`
`=x^5+(-x³y²+x³y²)+(x²y³-x²y³)+(-xy^4+xy^4)+y^5`
`=x^5+y^5`
`⇒VT=VP`
Vậy với mọi `x,y` ta luôn có `(x^4-x³y+x²y²-xy³+y^4)(x+y)=x^5+y^5`
