`1)(2x+3)²-(x+1)²`
`=(2x)²+2.2x.3+3²-(x²+2.x.1+1²)`
`=4x²+12x+9-x²-2x-1`
`=(4x²-x²)+(12x-2x)+(9-1)`
`=3x²+10x+8`
`13)(x²-1/3)(x^4+1/3x²+1/9)`
`=x² .x^4+x². 1/3x²+x². 1/9-1/3 . x^4-1/3 . 1/3x²-1/3 . 1/9`
`=x^6+1/3x^4+1/9x^2-1/3x^4-1/9x^2-1/27`
`=x^6+(1/3x^4-1/3x^4)+(-1/9x^2+1/9x^2)-1/27`
`=x^6-1/27`
`14)(1/3x+2y)(1/9x²-2/3xy+4y²)`
`=1/3x . 1/9x²-1/3x . 2/3xy+1/3x . 4y²+2y. 1/9x²-2y . 2/3xy+2y.4y²`
`=1/27x^3-2/9x^2y+4/3xy^2+2/9x^2y-4/3xy^2+8y^3`
`=1/27x^3+(-2/9x^2y+2/9x^2y)+(-4/3xy^2+4/3xy^2)+8y^3`
`=1/27x³+8y³`
