Desarrolla los productos y simplifica el res
$2$ $\left(a^{2}+3b\right)^{2}-\left(a^{2}-3b\right)^{2}=$
$3\left(2p-4\right)\left(2p+4\right)+8p\right)=$
$\dfrac {1} {2}y+\left(\dfrac {1} {2}y-1\right)^{3}-\left(\dfrac {1} {2}y^{2}+\dfrac {2} {3}\right)\left(\dfrac {1} {2}y^{2}+\dfrac {1} {3}\right)$