`a)VT=(x-y)(x^4+x³y+x²y²+xy³+y^4)`
`=x^5+x^4y+x³y²+x²y³+xy^4-x^4y-x³y²-x²y³-xy^4-y^5`
`=x^5+(x^4y-x^4y)+(x³y²-x³y²)+(x²y³-x²y³)+(xy^4-xy^4)-y^5`
`=x^5-y^5`
`=VP`
`⇒đpcm`
`b)VT=(x+y)(x^4-x³y+x²y²-y³+y^4)`
`=x^5-x^4y+x³y²-x²y³+xy^4+x^4y-x³y²+x²y³-xy^4+y^5`
`=x^5+(-x^4y+x^4y)+(x³y²-x³y²)+(-x²y³+x²y³)+(xy^4-xy^4)+y^5`
`=x^5+y^5`
`=VP`
`⇒đpcm`
`c)VT=(a+b)(a³-a²b+ab²-b³)`
`=a^4-a³b+a²b²-ab³+a³b-a²b²+ab³-b^4`
`=a^4+(-a³b+a³b)+(a²b²-a²b²)+(-ab³+ab³)-b^4`
`=a^4-b^4`
`=VP`
`⇒đpcm`
`d)VT=(a+b)(a²-ab+b²)`
`=a³-a²b+ab²+a²b-ab²+b³`
`=a³+(-a²b+a²b)+(ab²-ab²)+b³`
`=a³+b³`
`=VP`
`⇒đpcm`