Question

Use the Exponential Rule to find the indefinite integral. $$ \int 3 x e^{0.5 x^{2}} d x $$

Short answer

The indefinite integral \(\int 3 x e^{0.5 x^{2}} d x\) = \(3 e^{0.5x^2} + C\)

Step-by-step solution

Decision on Substitution

Notice that the integrand has a structure similar to \(u' e^{au}\). We are going to use the method of substitution. Here, we let \(u = 0.5x^2\) so that \(du = x dx\).

Rewrite the integral using substitution

By substituting \(u = 0.5x^2\) and \(du = x dx\), the integral can be rewritten in terms of \(u\) as \(\int{3 e^u du}\)

Perform the integration

Now, we can integrate to get \(3e^u + C\).

Substituting back

Finally, we substitute \(u = 0.5x^2\) back in to get the exact solution, \(3 e^{0.5x^2} + C\).

Key concepts

Exponential Rule Integration

The Exponential Rule for Integration is a staple in calculus used to find the antiderivative of exponential functions. When dealing with an indefinite integral of the form \( \int e^{kx} dx \), where \( k \) is a constant, the rule tells us the solution is \( \frac{1}{k}e^{kx} + C \), where \( C \) represents the constant of integration.

For more complex expressions, such as \( \int x e^{0.5 x^{2}} dx \), we observe the structure of the function and identify parts that resemble the derivative of the exponent. This approach allows us to use integrated exponential rules in combination with other techniques like substitution to easily find the indefinite integral.

U-Substitution Method

The U-Substitution Method, also known as integration by substitution, is akin to the 'change of variables' technique used to simplify an integral. It's commonly employed when an integral includes a function and its derivative. To perform u-substitution, we:

• Select a portion of the integrand to set as \( u \), which should make the integral simpler once substituted.
• Compute the differential \( du \) by taking the derivative of \( u \) with respect to \( x \) and solve for \( dx \).
• Rewrite the integral in terms of \( u \) and \( du \) and continue with integration on this simpler expression.
• After finding the antiderivative in terms of \( u \), substitute back the original expression set as \( u \) to get the solution in terms of the original variable.

This method simplifies many complex integrals and can often be the key to solving them where standard rules do not apply directly.

Integration by Substitution

Integration by substitution is a fundamental technique in calculus, serving as the counterpart to the chain rule for derivatives. When a function is too complicated to integrate directly, this method allows us to transform the integral into a simpler one that we’re capable of solving.

The process, briefly mentioned in the U-Substitution Method section, involves identifying a part of the function to replace with \( u \), finding \( du \) by differentiating \( u \) with respect to \( x \) and isolating \( dx \), and rewriting the integral in terms of \( u \) and \( du \). Integration is then performed on the simpler \( u \) form.

Applying the Method

If we have the integral \( \int 3 x e^{0.5 x^{2}} dx \), we notice that the exponent's derivative, \( x \), is present and thus, by letting \( u = 0.5x^2 \), we can transform this integral using the substitution method. Then, \( du = x dx \) simplifies the integration process to \( \int{3 e^u du} \) where the integration becomes straightforward.