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Ch. 8 - Techniques of Integration
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Non è quello che usi tu?Cambia libro di testo
Capitolo 8, Problema 8.6.38

In Exercises 27–40, use a substitution to change the integral into one you can find in the table. Then evaluate the integral.
∫ x^2 / √(x^2 - 4x + 5) dx

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1
Start by examining the expression inside the square root: \(x^2 - 4x + 5\). To simplify this, complete the square for the quadratic expression.
Rewrite \(x^2 - 4x + 5\) as \((x^2 - 4x + 4) + 1\), which simplifies to \((x - 2)^2 + 1\).
Use the substitution \(u = x - 2\), which implies $du = dx$. This changes the integral to an expression in terms of \(u\).
Rewrite the integral in terms of \(u\): replace \(x^2\) with \((u + 2)^2\) and \(\sqrt{x^2 - 4x + 5}\) with \(\sqrt{u^2 + 1}\). The integral becomes \(\int \frac{(u + 2)^2}{\sqrt{u^2 + 1}} \, du\).
Expand \((u + 2)^2\) to \(u^2 + 4u + 4\) and split the integral into three separate integrals: \(\int \frac{u^2}{\sqrt{u^2 + 1}} \, du + 4 \int \frac{u}{\sqrt{u^2 + 1}} \, du + 4 \int \frac{1}{\sqrt{u^2 + 1}} \, du\). Each of these can be found in standard integral tables.

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Substitution Method in Integration

The substitution method involves changing variables in an integral to simplify the integrand into a form that is easier to integrate. By choosing an appropriate substitution, often based on the inner function or expression, the integral can be transformed into a standard form found in integral tables.
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Completing the Square

Completing the square is a technique used to rewrite quadratic expressions in the form ax^2 + bx + c as (x - h)^2 + k. This form simplifies the integrand, especially under square roots, making it easier to identify substitutions or match standard integral forms.
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Using Integral Tables

Integral tables list standard integrals and their antiderivatives, providing quick references for common integral forms. After substitution and simplification, matching the integral to a form in the table allows for direct evaluation without performing integration from first principles.
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