Math Problem Statement

Let g(x) = ∫ from -2 to x of f(t) dt. The absolute minimum of g(x) on [-2, 2] occurs at which of the following?

Solution

Problem Overview:

We are given a graph of f(x)f(x) on the interval [2,2][-2, 2], and we define g(x)=2xf(t)dtg(x) = \int_{-2}^x f(t) \, dt. The goal is to find where the absolute minimum of g(x)g(x) occurs on [2,2][-2, 2].


Step-by-step Solution:

1. Understand g(x)g(x):

  • g(x)g(x) represents the accumulated area under the curve f(t)f(t) from 2-2 to xx.
  • Positive areas (above the xx-axis) increase g(x)g(x), and negative areas (below the xx-axis) decrease g(x)g(x).

2. Analyze the graph of f(x)f(x):

  • From x=2x = -2 to x=1x = -1: f(x)f(x) is negative and linear (slope = 1). The area here is a triangle below the xx-axis with base 1 and height 1: Area=12(1)(1)=12.\text{Area} = -\frac{1}{2}(1)(1) = -\frac{1}{2}.

  • From x=1x = -1 to x=1x = 1: f(x)f(x) is positive and linear (slope = 1). The area here is a triangle above the xx-axis with base 2 and height 2: Area=12(2)(2)=2.\text{Area} = \frac{1}{2}(2)(2) = 2.

  • From x=1x = 1 to x=2x = 2: f(x)f(x) is constant and equal to 1. The area here is a rectangle: Area=(1)(1)=1.\text{Area} = (1)(1) = 1.


3. Compute g(x)g(x) at key points:

To identify the absolute minimum, compute g(x)g(x) at key points where x=2,1,0,1,2x = -2, -1, 0, 1, 2.

  1. At x=2x = -2: g(2)=22f(t)dt=0g(-2) = \int_{-2}^{-2} f(t) \, dt = 0.

  2. At x=1x = -1: g(1)=21f(t)dt=12g(-1) = \int_{-2}^{-1} f(t) \, dt = -\frac{1}{2}.

  3. At x=0x = 0: g(0)=20f(t)dt=12+12(1)(1)=0g(0) = \int_{-2}^0 f(t) \, dt = -\frac{1}{2} + \frac{1}{2}(1)(1) = 0.

  4. At x=1x = 1: g(1)=21f(t)dt=12+2=32g(1) = \int_{-2}^1 f(t) \, dt = -\frac{1}{2} + 2 = \frac{3}{2}.

  5. At x=2x = 2: g(2)=22f(t)dt=12+2+1=52g(2) = \int_{-2}^2 f(t) \, dt = -\frac{1}{2} + 2 + 1 = \frac{5}{2}.


4. Determine the absolute minimum:

  • From the computed values, g(x)g(x) has the following values: g(2)=0,g(1)=12,g(0)=0,g(1)=32,g(2)=52.g(-2) = 0, \quad g(-1) = -\frac{1}{2}, \quad g(0) = 0, \quad g(1) = \frac{3}{2}, \quad g(2) = \frac{5}{2}.
  • The absolute minimum occurs at x=1x = -1, where g(x)=12g(x) = -\frac{1}{2}.

Final Answer:

The absolute minimum of g(x)g(x) on [2,2][-2, 2] occurs at x=1\boxed{x = -1}.


Do you want further clarification or details?


Expanding the Concept:

  1. What happens to g(x)g(x) at other points on the interval [2,2][-2, 2]?
  2. Why does the minimum of g(x)g(x) correspond to the most negative accumulated area?
  3. How would g(x)g(x) behave if f(x)f(x) were entirely negative on [2,2][-2, 2]?
  4. What does the Fundamental Theorem of Calculus say about g(x)g'(x) in this problem?
  5. How could we solve this problem without explicitly calculating areas?

Tip:

Always relate the graph of f(x)f(x) to changes in g(x)g(x): positive f(x)f(x) increases g(x)g(x), while negative f(x)f(x) decreases it.

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Math Problem Analysis

Mathematical Concepts

Definite integrals
Accumulated area under a curve
Graphical analysis of functions

Formulas

g(x) = ∫ from -2 to x of f(t) dt

Theorems

Fundamental Theorem of Calculus

Suitable Grade Level

Grades 11-12