Calculus Examples

$4 x \cdot \ln (x)$

Step 1

Write $4 x \cdot \ln (x)$ as a function.

$f (x) = 4 x \cdot \ln (x)$

Step 2

The function $F (x)$ can be found by finding the indefinite integral of the derivative $f (x)$ .

$F (x) = \int f (x) d x$

Step 3

Set up the integral to solve.

$F (x) = \int 4 x \cdot \ln (x) d x$

Step 4

Since $4$ is constant with respect to $x$ , move $4$ out of the integral.

$4 \int x \cdot \ln (x) d x$

Step 5

Integrate by parts using the formula $\int u d v = u v - \int v d u$ , where $u = \ln (x)$ and $d v = x$ .

$4 (\ln (x) (\frac{1}{2} x^{2}) - \int \frac{1}{2} x^{2} \frac{1}{x} d x)$

Step 6

Simplify.

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Step 6.1

Combine $\frac{1}{2}$ and $x^{2}$ .

$4 (\ln (x) \frac{x^{2}}{2} - \int \frac{1}{2} x^{2} \frac{1}{x} d x)$

Step 6.2

Combine $\ln (x)$ and $\frac{x^{2}}{2}$ .

$4 (\frac{\ln (x) x^{2}}{2} - \int \frac{1}{2} x^{2} \frac{1}{x} d x)$

Step 6.3

Combine $\frac{1}{2}$ and $x^{2}$ .

$4 (\frac{\ln (x) x^{2}}{2} - \int \frac{x^{2}}{2} \cdot \frac{1}{x} d x)$

Step 6.4

Multiply $\frac{x^{2}}{2}$ by $\frac{1}{x}$ .

$4 (\frac{\ln (x) x^{2}}{2} - \int \frac{x^{2}}{2 x} d x)$

Step 6.5

Cancel the common factor of $x^{2}$ and $x$ .

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Step 6.5.1

Factor $x$ out of $x^{2}$ .

$4 (\frac{\ln (x) x^{2}}{2} - \int \frac{x \cdot x}{2 x} d x)$

Step 6.5.2

Cancel the common factors.

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Step 6.5.2.1

Factor $x$ out of $2 x$ .

$4 (\frac{\ln (x) x^{2}}{2} - \int \frac{x \cdot x}{x \cdot 2} d x)$

Step 6.5.2.2

Cancel the common factor.

$4 (\frac{\ln (x) x^{2}}{2} - \int \frac{x \cdot x}{x \cdot 2} d x)$

Step 6.5.2.3

Rewrite the expression.

$4 (\frac{\ln (x) x^{2}}{2} - \int \frac{x}{2} d x)$

Step 7

Since $\frac{1}{2}$ is constant with respect to $x$ , move $\frac{1}{2}$ out of the integral.

$4 (\frac{\ln (x) x^{2}}{2} - (\frac{1}{2} \int x d x))$

Step 8

By the Power Rule, the integral of $x$ with respect to $x$ is $\frac{1}{2} x^{2}$ .

$4 (\frac{\ln (x) x^{2}}{2} - \frac{1}{2} (\frac{1}{2} x^{2} + C))$

Step 9

Simplify the answer.

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Step 9.1

Combine $\frac{1}{2}$ and $x^{2}$ .

$4 (\frac{\ln (x) x^{2}}{2} - \frac{1}{2} (\frac{x^{2}}{2} + C))$

Step 9.2

Rewrite $4 (\frac{\ln (x) x^{2}}{2} - \frac{1}{2} (\frac{x^{2}}{2} + C))$ as $4 (\frac{\ln (x) x^{2}}{2} - \frac{x^{2}}{4}) + C$ .

$4 (\frac{\ln (x) x^{2}}{2} - \frac{x^{2}}{4}) + C$

Step 9.3

Reorder terms.

$4 (\frac{1}{2} \ln (x) x^{2} - \frac{1}{4} x^{2}) + C$

Step 10

The answer is the antiderivative of the function $f (x) = 4 x \cdot \ln (x)$ .

$F (x) =$ $4 (\frac{1}{2} \ln (x) x^{2} - \frac{1}{4} x^{2}) + C$