The equation in the image appears to represent the composition of two functions and the evaluation of one of them at a specific point. Let's break it down:

The notation $(f \circ g)(x)$ means the composition of functions $f$ and $g$, and it is defined as:

$(f \circ g)(x) = f(g(x))$

In the image, the equation proceeds as follows:

1. $(f \circ g)(x) = f(g(x))$
2. $f(g(x)) = f(x^2 - 9)$

This suggests that the function $g(x)$ is defined as:

$g(x) = x^2 - 9$

Thus, the composition of $f$ and $g$, evaluated at $x$, is given by substituting $g(x)$ into $f$:

$(f \circ g)(x) = f(x^2 - 9)$

Do you need help with a specific part of this problem, or would you like further details on function composition or solving this kind of expression?

Here are five related questions that can extend your understanding:

1. How do you find the composition of two arbitrary functions $f$ and $g$?
2. If $f(x) = 3x + 2$ and $g(x) = x^2 - 9$, what is $(f \circ g)(x)$?
3. What are the conditions for two functions to be composed?
4. How can the domain of $(f \circ g)(x)$ be affected by the domain of $g(x)$?
5. How does the composition of functions differ from multiplication of functions?

Tip: Always check the domain of both functions when composing them, as the domain of the composition is restricted by the domain of the inner function.