`#huy`
`a) (x+2)^2-(x+3)(x-3)+10`
`=x^2+4x+4-(x^2-9)+10`
`=x^2+4x+4-x^2+9+10`
`=4x+23`
`b) (x+5)(x^2-5x+25)-x(x-4)^2+16x`
`=(x+5)(x^2-5x+5^2)-x(x^2-8x+16)+16x`
`=x^3-5^3-x^3+8x^2-16x+16x`
`=8x^2+125`
`c) (x-2y)^3-(x+2y)(x^2-2xy+4y^2)+6x^2y`
`=x^2-6x^2y+12xy^2-8y^3-[x^3-(2y)^3]+6x^2y`
`=x^3+12xy^2-8y^3-x^3-8y^3`
`=12xy^2-16y^3`