Solving Integral: Different Answer with U-Substitution

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In summary, U-Substitution is a technique used in integration that involves substituting a variable, called u, in the integrand to simplify the integral. It can sometimes lead to a different answer because it involves changing the variable of integration, which can affect the limits of integration and the integrand itself. U-Substitution is typically used when the integrand involves a function raised to a power, a trigonometric function, or an exponential function, and can be used for both indefinite and definite integrals. However, when using U-Substitution for definite integrals, it is important to adjust the limits of integration accordingly. If U-Substitution does not lead to a simpler integral, it may be necessary to use other techniques
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this integral can be solved without u-subsitution however, I get a different answer when I use u-sub.

[tex]\int \frac{6}{x-6} dx [/tex]

[tex]u=x-6[/tex]

[tex]du=dx[/tex]

[tex]\int \frac{1}{6u}=\frac{1}{6}ln(x-6)[/tex]

if U-sub wasnt used, then the answer would be 6ln(x-6)

what am I doing wrong in the subsitution?
 
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With the substitution, the integral is:

[tex]\int \frac{6}{u} du[/tex]

not

[tex]\int \frac{1}{6u} du[/tex]
 

FAQ: Solving Integral: Different Answer with U-Substitution

What is U-Substitution?

U-Substitution is a technique used in integration that involves substituting a variable, called u, in the integrand to simplify the integral.

Why do I get a different answer when using U-Substitution?

U-Substitution can sometimes lead to a different answer because it involves changing the variable of integration, which can affect the limits of integration and the integrand itself. It is important to carefully consider these changes when using U-Substitution.

How do I know when to use U-Substitution?

U-Substitution is typically used when the integrand involves a function raised to a power, a trigonometric function, or an exponential function. It is also useful when the integrand is a product or a quotient of these types of functions.

Can I use U-Substitution for definite integrals?

Yes, U-Substitution can be used for both indefinite and definite integrals. However, when using U-Substitution for definite integrals, it is important to adjust the limits of integration accordingly.

What should I do if U-Substitution does not work?

If U-Substitution does not lead to a simpler integral, it may be necessary to use other techniques such as integration by parts or partial fraction decomposition. It is also important to check for any mistakes in the substitution process.

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