Let $f(x) = x^2 + 6x + c$ for all real numbers $x$, where $c$ is some real number.  For what values of $c$ does $f(f(x))$ have exactly $3$ distinct real roots?
Question:
Let $f(x) = x^2 + 6x + c$ for all real numbers $x$, where $c$ is some real number.  For what values of $c$ does $f(f(x))$ have exactly $3$ distinct real roots?
Answer:
Let's think step by step.

user
\frac{11 - \sqrt{13}}{2}
Let $f(x) = x^2 + 6x + c$ for all real numbers $x$, where $c$ is some real number.  For what values of $c$ does $f(f(x))$ have exactly $3$ distinct real roots?
train