Solve Quadratic Function f(x) = x²: Finding Input When f(x) = 9

To solve this problem, we'll follow these steps:

• Step 1: Set up the equation $x^2 = 9$.
• Step 2: Solve for $x$ by taking the square root of both sides.
• Step 3: Choose the correct answer from the given options.

Now, let's work through each step:
Step 1: We set $x^2 = 9$.
Step 2: Solving for $x$, we take the square root of both sides: $x = \pm \sqrt{9}$.
Step 3: This yields two solutions: $x = 3$ and $x = -3$.

Comparing these values with the given choices:

• Choice 1: $f(3)$ corresponds to $x = 3$.
• Choice 3: $f(-3)$ corresponds to $x = -3$.

Both choices $f(3)$ and $f(-3)$ are correct, leading us to select the combined choice: Answer A+C.