2a^2(3a^2-2a+1)+4a^3
=6a⁴-4a³+2a²+4a³
=6a⁴+2a²

(-2x^2y+6x^3y^4-8xy)÷(-2xy)
=(-2xy)(x-3x²y³+4)÷(-2xy)
=x-3x²y³+4

(2x+y)^2-(2x+3y)(3x-3y)
=4x²+4xy+y²-(6x²-9y²+3xy)
=4x²+4xy+y²-6x²+9y²-3xy
=-2x²+xy+10y²