Question 21
For how many values of the coefficient $a$ do the equations $$
\begin{aligned} x^2+ax+1&=0,\\ x^2-x-a&=0 \end{aligned}
$$ have a common real solution?
\begin{aligned} x^2+ax+1&=0,\\ x^2-x-a&=0 \end{aligned}
$$ have a common real solution?