[tex]-5a-(-4)a^{3}-2b^{2}=\boxed{-5a+4a^{3}-2b^{2}}\\\\-5a+2a^{3}b^{2} \neq -5a+4a^{3}-2b^{2}\\\\-5a+2a\cdot2a^{2}-2b^{2} =\boxed{ -5+4a^{3}-2b^{2}}\\\\5a-4a^{3}-2b^{2}\neq -5+4a^{3}-2b^{2}\\\\-5a+4a^{3}+2b(-b) = \boxed{-5a+4a^{3}-2b^{2}}[/tex]
