Question 28
Find all values of the real parameter $a$ for which all solutions of the equation
$$
x^{4}-2 x^{3}-3 x^{2}-4 a x-a^{2}=0
$$
are real. For the values found, solve the equation.
$$
x^{4}-2 x^{3}-3 x^{2}-4 a x-a^{2}=0
$$
are real. For the values found, solve the equation.