`a)A=(3+4y)²+2(3+4y)(3-4y)+(4y+3)²`
`=9+24y+16y²+2(9-16y²)+16y²+24y+9`
`=9+24y+16y²+18-32y²+16y²+24y+9`
`=(16y²-32y²+16y²)+(24y+24y)+(9+18+9)`
`=48y+36`
`b)B=3(x-1)²-(x+1)²+2(x-3)(x+3)-(2x+3)²`
`=3(x²-2x+1)-(x²+2x+1)+2(x²-9)-(4x²+12x+9)`
`=3x²-6x+3-x²-2x-1+2x²-18-4x²-12x-9`
`=(3x²-x²+2x²-4x²)+(-6x-2x-12x)+(3-1-18-9)`
`=-20x-25`
`c)C=(x+2)³+(2x-1)³-18x-9(x³-2)`
`=x³+6x²+12x+8+8x³-12x²+6x-1-18x-9x³+18`
`=(x³+8x³-9x³)+(6x²-12x²)+(12x+6x-18x)+(8-1+18)`
`=-6x²+25`
`d)D=(2x-1)³-6x(2x-1)²+12x²(2x-1)-8x³`
`=(2x-1)³-3.(2x-1)².2x+3.(2x-1).(2x)²-(2x)³`
`=(2x-1-2x)³`
`=(-1)³`
`=-1`
`e)E=(x+y)³-(x-y)³-2y(y²+3x²)`
`=x³+3x²y+3xy²+y³-(x³-3x²y+3xy²-y³)-2y³-6x²y`
`=x³+3x²y+3xy²+y³-x³+3x²y-3xy²+y³-2y³-6x²y`
`=(x³-x³)+(3x²y+3x²y-6x²y)+(3xy²-3xy²)+(y³+y³-2y³)`
`=0`
`f)F=(x+y)³-(x³+y³)-3xy(x+y)`
`=x³+3x²y+3xy²+y³-x³-y³-3x²y-3xy²`
`=(x³-x³)+(3x²y-3x²y)+(3xy²-3xy²)+(y³-y³)`
`=0`