$12\right)$ $a^{2}-6ab^{2}+9b^{4}=$
$13\right)$ $16+40x^{2}+25x^{4}=$
$14\right)$ $a^{2}-10a+25=$
15) $36+12m^{2}+m^{4}=$
16) $4a^{2}-12ab+9b^{2}=$
$17\right)$ $9m^{2}n^{2}+42mn+49=$
18) $1-2a^{3}+a^{6}=$
19) $18a^{4}+81+a^{8}=$
$20\right)$ $-2a^{3}b^{3}+a^{6}+b^{6}$ =
$21\right)$ $4x^{2}+9y^{2}-12xy=$
$22\right)$ $9b^{2}-30a^{2}b+25a^{4}$ :