`1)(a+1)³`
`=a³+3.a².1+3.a.1²+1³`
`=a³+3a²+3a+1`
`2)(a+2)³`
`=a³+3.a².2+3.a.2²+2³`
`=a³+6a²+12a+8`
`3)(x+1)³`
`=x³+3.x².1+3.x.1²+1³`
`=x³+3x²+3x+1`
`6)(a-1)³`
`=a³-3.a².1+3.a.1²-1³`
`=a³-3a²+3a-1`
`9)(x-4)³`
`=x³-3.x².4+3.x.4²-4³`
`=x³-12x²+48x-64`
`10)(2x-3y)³`
`=(2x)³-3.(2x)².3y+3.2x.(3y)²-(3y)³`
`=8x³-36x²y+54xy²-27y³`
`11)(x-1)(x²+x+1)`
`=(x-1)(x²+x.1+1²)`
`=x³-1³`
`=x³-1`
`16)(x+1)(x²-x+1)`
`=(x+1)(x²-x.1+1²)`
`=x³+1³`
`=x³+1`
`19)(x+5)(x²-5x+25)`
`=(x+5)(x²-x.5+5²)`
`=x³+5³`
`=x³+125`
`20)(x+1/2)(x²-x/2+1/4)`
`=(x+1/2)[x²-x. 1/2+(1/2)^2]`
`=x³+(1/2)^3`
`=x³+1/8`