How are the general skills for complete factorization of arbitrary homogeneous order polynomials in $\mathbb{C}$ ?
For example:
$1.$ $a^2+b^2+c^2$
$2.$ $a^2+b^2-c^2$
$3.$ $a^2+b^2+c^2+d^2$
$4.$ $a^2+b^2+c^2-d^2$
$5.$ $pa^2+qb^2+rc^2$ , where $p,q,r$ are non-zero constants
$6.$ $pa^2+qb^2+rc^2+sd^2$ , where $p,q,r,s$ are non-zero constants