Math Problem Statement

Let f(x) = { 0 if x < -3, 3 if -3 ≤ x < -1, -4 if -1 ≤ x < 4, 0 if x ≥ 4 } and g(x) = ∫ from -3 to x of f(t) dt. Determine the values of g(-4), g(-2), g(0), g(5), and the absolute maximum of g(x).

Solution

Let’s analyze the problem step by step.

Given:

  1. f(x)f(x): \begin{cases} 0 & \text{if } x < -3, \\ 3 & \text{if } -3 \leq x < -1, \\ -4 & \text{if } -1 \leq x < 4, \\ 0 & \text{if } x \geq 4. \end{cases}$$
  2. g(x)=3xf(t)dtg(x) = \int_{-3}^{x} f(t) \, dt.

We need to calculate the following:

  • (a) g(4)g(-4)
  • (b) g(2)g(-2)
  • (c) g(0)g(0)
  • (d) g(5)g(5)
  • (e) The absolute maximum of g(x)g(x).

Step 1: Analyze the function f(x)f(x)

  • On the interval (,3)(-\infty, -3): f(x)=0f(x) = 0.
  • On the interval [3,1)[-3, -1): f(x)=3f(x) = 3.
  • On the interval [1,4)[-1, 4): f(x)=4f(x) = -4.
  • On the interval [4,)[4, \infty): f(x)=0f(x) = 0.

Step 2: Compute g(x)g(x) for each case

(a) g(4)g(-4):

Since x=4<3x = -4 < -3, f(t)=0f(t) = 0 over the interval [3,4][-3, -4]. Thus: g(4)=34f(t)dt=0.g(-4) = \int_{-3}^{-4} f(t) \, dt = 0.


(b) g(2)g(-2):

Here 32<1-3 \leq -2 < -1, so f(t)=3f(t) = 3 over the interval [3,2][-3, -2]. Compute the integral: g(2)=323dt=3[t]32=3(2(3))=31=3.g(-2) = \int_{-3}^{-2} 3 \, dt = 3 \cdot [t]_{-3}^{-2} = 3 \cdot (-2 - (-3)) = 3 \cdot 1 = 3.


(c) g(0)g(0):

Here 0[1,4)0 \in [-1, 4), so split the integral into two parts:

  1. Over [3,1][-3, -1], f(t)=3f(t) = 3.
  2. Over [1,0][-1, 0], f(t)=4f(t) = -4.

First, compute the contribution from [3,1][-3, -1]: 313dt=3(1(3))=32=6.\int_{-3}^{-1} 3 \, dt = 3 \cdot (-1 - (-3)) = 3 \cdot 2 = 6.

Next, compute the contribution from [1,0][-1, 0]: 104dt=4(0(1))=41=4.\int_{-1}^{0} -4 \, dt = -4 \cdot (0 - (-1)) = -4 \cdot 1 = -4.

Adding these contributions: g(0)=6+(4)=2.g(0) = 6 + (-4) = 2.


(d) g(5)g(5):

Here x=54x = 5 \geq 4, so split the integral into three parts:

  1. Over [3,1][-3, -1], f(t)=3f(t) = 3.
  2. Over [1,4][-1, 4], f(t)=4f(t) = -4.
  3. Over [4,5][4, 5], f(t)=0f(t) = 0.

The first two parts were already computed:

  • From [3,1][-3, -1]: 313dt=6\int_{-3}^{-1} 3 \, dt = 6,
  • From [1,4][-1, 4]: 144dt=4(4(1))=45=20\int_{-1}^{4} -4 \, dt = -4 \cdot (4 - (-1)) = -4 \cdot 5 = -20.

Adding these: g(5)=6+(20)=14.g(5) = 6 + (-20) = -14.


(e) Absolute maximum of g(x)g(x):

The function g(x)g(x) increases when f(x)>0f(x) > 0 (on [3,1][-3, -1]) and decreases when f(x)<0f(x) < 0 (on [1,4][-1, 4]). The maximum occurs at x=1x = -1: g(1)=31f(t)dt=313dt=6.g(-1) = \int_{-3}^{-1} f(t) \, dt = \int_{-3}^{-1} 3 \, dt = 6.

Thus, the absolute maximum of g(x)g(x) is: Maximum value=6at x=1.\text{Maximum value} = 6 \quad \text{at } x = -1.


Final Answers:

(a) g(4)=0g(-4) = 0
(b) g(2)=3g(-2) = 3
(c) g(0)=2g(0) = 2
(d) g(5)=14g(5) = -14
(e) The absolute maximum occurs at x=1x = -1 and is 66.


Would you like a graph of f(x)f(x) or further clarification on any step?

Here are 5 follow-up questions to deepen understanding:

  1. How does the sign of f(x)f(x) affect the behavior of g(x)g(x)?
  2. What is the physical interpretation of g(x)g(x) in terms of the area under the curve of f(x)f(x)?
  3. How would g(x)g(x) behave if f(x)f(x) were shifted to the right?
  4. How can you determine the critical points of g(x)g(x) using f(x)f(x)?
  5. What happens to g(x)g(x) as xx \to -\infty or xx \to \infty?

Tip: For piecewise-defined integrals, always split the integral according to intervals where the function is constant or changes behavior!

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Math Problem Analysis

Mathematical Concepts

Piecewise Functions
Definite Integrals
Area Under a Curve
Function Behavior Analysis

Formulas

g(x) = ∫ from -3 to x of f(t) dt
Area of a rectangle: A = width × height

Theorems

Fundamental Theorem of Calculus

Suitable Grade Level

Grades 11-12 (Calculus AB level)