Math Problem Statement

Evaluate the definite integral \( \int_{1}^{2} \left( 8x^{-2} - 4 \right) dx \).

Solution

The integral shown in the image is:

12(8x24)dx.\int_{1}^{2} \left( 8x^{-2} - 4 \right) dx.

Let's evaluate it step by step.


Step 1: Separate the integrals

We can split the integral into two parts: 12(8x24)dx=128x2dx124dx.\int_{1}^{2} \left( 8x^{-2} - 4 \right) dx = \int_{1}^{2} 8x^{-2} dx - \int_{1}^{2} 4 dx.


Step 2: Compute each integral

  1. For 8x2dx\int 8x^{-2} dx: The integral of x2x^{-2} is: x2dx=x1=1x.\int x^{-2} dx = -x^{-1} = -\frac{1}{x}. Therefore: 8x2dx=8(1x)=8x.\int 8x^{-2} dx = 8 \cdot \left(-\frac{1}{x}\right) = -\frac{8}{x}.

  2. For 4dx\int 4 dx: The integral of a constant 44 is: 4dx=4x.\int 4 dx = 4x.


Step 3: Evaluate the definite integrals

  1. Evaluate 8x-\frac{8}{x} from 1 to 2: [8x]12=(82)(81)=4+8=4.\left[-\frac{8}{x}\right]_{1}^{2} = \left(-\frac{8}{2}\right) - \left(-\frac{8}{1}\right) = -4 + 8 = 4.

  2. Evaluate 4x4x from 1 to 2: [4x]12=(42)(41)=84=4.\left[4x\right]_{1}^{2} = \left(4 \cdot 2\right) - \left(4 \cdot 1\right) = 8 - 4 = 4.


Step 4: Combine results

Now combine the results of the two integrals: 12(8x24)dx=44=0.\int_{1}^{2} \left( 8x^{-2} - 4 \right) dx = 4 - 4 = 0.


Final Answer:

0\boxed{0}

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Math Problem Analysis

Mathematical Concepts

Calculus
Definite Integrals
Polynomial Integration

Formulas

Integral of power: \( \int x^n dx = \frac{x^{n+1}}{n+1} + C \), for \( n \neq -1 \)
Integral of a constant: \( \int k dx = kx \)

Theorems

Fundamental Theorem of Calculus

Suitable Grade Level

Grades 11-12 or early university