$\text{a)}{\left(3x^2+10\right)}^2={\left(3x^2\right)}^2+2\cdot 3x^2\cdot 10+{10}^2=9x^4+60x^2+100$

$\text{b)}{\left(2x^3-\sqrt{6}\right)}^2={\left(2x^3\right)}^2-2\cdot 2x^3\cdot \sqrt{6}+{\sqrt{6}}^2=4x^6-4\sqrt{6}{x}^3+6$