`17)`
`(2x-3)(4x^2+6x+9)-(2x-1)^3+(3x+1)(9x^2-3x+1)`
`=(2x)^3-3^3-(8x^3-12x^2+6x-1)+(3x)^3+1^3`
`=8x^3-27-8x^3+12x^2-6x+1+27x^3+1`
`=(8x^3-8x^3+27x^3)+12x^2-6x+(1+1-27)`
`=27x^3+12x^2-6x-25`
`18)`
`(2x+1)^3-(5x+2)(25x^2-10x+4)+(x-5)^3-(3x+5)^3`
`=(8x^3+12x^2+6x+1)-[(5x)^3+2^3]+(x^3-15x^2+75x-125)-(27x^3+135x^2+225x+125)`
`=8x^3+12x^2+6x+1-125x^3-8+x^3-15x^2+75x-125-27x^3-135x^2-225x-125`
`=(8x^3-125x^3-27x^3+x^3)+(12x^2-15x^2-135x^2)+(6x+75x-225x)+(1-8-125-125)`
`=-143x^3-138x^2-144x-257`
`19)`
`(3x-2y)^3-(4x-5y)(16x^2+20xy+25y^2)+(2x+y)^3`
`=(27x^3-54x^2y+36xy^2-8y^3)-[(4x)^3-(5y)^3]+(8x^3+12x^2y+6xy^2+y^3)`
`=27x^3-54x^2y+36xy^2-8y^3-64x^3+125y^3+8x^3+12x^2y+6xy^2+y^3`
`=(27x^3-64x^3+8x^3)+(-54x^2y+12x^2y)+(36xy^2+6xy^2)+(125y^3-8y^3+y^3)`
`=-29x^3-42x^2y+42xy^2+118y^3`
`20)`
`(x+3y)^3+(3x+2y)(9x^2-6xy+4y^2)-(2y-3x)^3`
`=(x^3+9x^2y+27xy^2+27y^3)+[(3x)^3+(2y)^3]-(-27x^3+54x^2y-36xy^2+8y^3)`
`=x^3+9x^2y+27xy^2+27y^3+27x^3+8y^3+27x^3-54x^2y+36xy^2-8y^3`
`=(x^3+27x^3+27x^3)+(9x^2y-54x^2y)+(27xy^2+36xy^2)+(8y^3-8y^3)+27y^3`
`=55x^3-45x^2y+63xy^2+27y^3`
