g(f(4)) = g(9) = 9^2 - 3 = 81 - 3 = 78 - Veritas Home Health

Understanding the Context

What Does g(f(4)) Mean?

In mathematics, g(f(x)) denotes function composition — applying function f first, then function g to the result. Here, g(f(4)) means:

1. Evaluate f(4)
   
2. Use that output as the input to g — so compute g(f(4)) = g(n) where n = f(4)

But in the expression g(f(4)) = g(9) = 78, we’re told this entire process simplifies numerically to 78, even though f(4) may not literally equal 9. Why? Because g behaves in a way that maps f(4) directly to 78 regardless of internal values — a clue about g’s defined behavior.

Key Insights

The Given Equation:

g(f(4)) = g(9) = 78

This tells us three key pieces of information:

1. Applying f to 4 produces some value, say f(4) = ?
   
2. Applying g to that value gives g(f(4)) = 78
   
3. But g(9) = 78 — so when input is 9, output is 78

Since g(f(4)) = g(9) and both equal 78, we can infer:

Final Thoughts

✅ f(4) = 9 — this creates consistency between composition and direct evaluation.

Thus, g(9) = 78 by definition.

Step-by-Step Breakdown

| Step | Expression | Explanation |
|------|----------------------|-------------|
| 1 | Let x = 4 | Start the composition with input → 4 |
| 2 | Evaluate f(4) | Say f(4) = 9 (key insight) |
| 3 | Apply g: g(9) | Now substitute result into g → g(9) |
| 4 | Final value: 78 | From problem statement |

So, g(f(4)) = g(9) = 78 confirms that f(4) = 9 is assumed, and g(9) directly outputs 78.