- The function is increasing on \((0, 30)\) and decreasing on \((30, 55)\) based on the sign of the first derivative.
- The relative and absolute maximum occurs at \(x = 30\).
- The function is concave up on \((0, 15)\) and concave down on \((15, 55)\), with an inflection point at \(x = 15\).
- Final results:
AIncreasing on: \(\boxed{(0, 30)}\), Decreasing on: \(\boxed{(30, 55)}\)
B\(\boxed{30}\)
CConcave up on: \(\boxed{(0, 15)}\), Concave down on: \(\boxed{(15, 55)}\)
D\(\boxed{15}\)
Explanation
- Problem Analysis
The revenue function is given by \(S(x) = -0.012x^3 + 0.54x^2 + 120\) for the domain \(x \in [0, 55]\). This is a cubic polynomial function, which is continuous and differentiable throughout its domain. We will analyze its behavior using the first and second derivatives to determine its monotonicity, extrema, and concavity.
- Increasing and Decreasing Intervals
To find where the revenue is increasing or decreasing, we first compute the first derivative:
\(S'(x) = \frac{d}{dx}(-0.012x^3 + 0.54x^2 + 120) = -0.036x^2 + 1.08x\).
Setting \(S'(x) = 0\):
\(-0.036x(x - 30) = 0\).
The critical points are \(x = 0\) and \(x = 30\).
Testing intervals within \([0, 55]\):
- For \(x \in (0, 30)\), pick \(x=10\): \(S'(10) = -0.036(100) + 1.08(10) = -3.6 + 10.8 = 7.2 > 0\), so the function is increasing.
- For \(x \in (30, 55)\), pick \(x=40\): \(S'(40) = -0.036(1600) + 1.08(40) = -57.6 + 43.2 = -14.4 < 0\), so the function is decreasing.
Thus, \(S\) is increasing on \((0, 30)\) and decreasing on \((30, 55)\).
- Finding the Maximum Revenue
We evaluate the function \(S(x)\) at the critical points and boundaries:
- \(S(0) = 120\)
- \(S(30) = -0.012(30^3) + 0.54(30^2) + 120 = -0.012(27000) + 0.54(900) + 120 = -324 + 486 + 120 = 282\)
- \(S(55) = -0.012(55^3) + 0.54(55^2) + 120 = -0.012(166375) + 0.54(3025) + 120 = -1996.5 + 1633.5 + 120 = -243\)
Comparing these values, the maximum revenue occurs at \(x = 30\). This point is both a relative and an absolute maximum.
- Concavity and Inflection Point
To find the concavity, we compute the second derivative:
\(S''(x) = \frac{d}{dx}(-0.036x^2 + 1.08x) = -0.072x + 1.08\).
Setting \(S''(x) = 0\) gives \(0.072x = 1.08\), so \(x = 15\).
Testing intervals:
- For \(x \in (0, 15)\), pick \(x=1\): \(S''(1) = -0.072(1) + 1.08 = 1.008 > 0\), so the function is concave up.
- For \(x \in (15, 55)\), pick \(x=20\): \(S''(20) = -0.072(20) + 1.08 = -1.44 + 1.08 = -0.36 < 0\), so the function is concave down.
The inflection point is at \(x = 15\).
- Final Answer Summary
The final results are:
AIncreasing on: \((0, 30)\), Decreasing on: \((30, 55)\).
BRelative and absolute maximum at \(x = 30\).
CConcave up on: \((0, 15)\), Concave down on: \((15, 55)\).
DInflection point at \(x = 15\).
Examples
A manager can use this revenue analysis to determine the optimal budget allocation for a marketing campaign. By identifying the budget value where the marginal revenue becomes zero (the maximum point of the revenue function), the company avoids overspending on a campaign that yields diminishing returns. This strategic use of calculus helps in maximizing profitability and efficient resource management.