Calculus Examples

$\int_{0}^{\frac{π}{4}} \sin (4 x) d x$

Step 1

Let $u = 4 x$ . Then $d u = 4 d x$ , so $\frac{1}{4} d u = d x$ . Rewrite using $u$ and $d$ $u$ .

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Step 1.1

Let $u = 4 x$ . Find $\frac{d u}{d x}$ .

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Step 1.1.1

Differentiate $4 x$ .

$\frac{d}{d x} [4 x]$

Step 1.1.2

Since $4$ is constant with respect to $x$ , the derivative of $4 x$ with respect to $x$ is $4 \frac{d}{d x} [x]$ .

$4 \frac{d}{d x} [x]$

Step 1.1.3

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$4 \cdot 1$

Step 1.1.4

Multiply $4$ by $1$ .

$4$

Step 1.2

Substitute the lower limit in for $x$ in $u = 4 x$ .

$u_{lower} = 4 \cdot 0$

Step 1.3

Multiply $4$ by $0$ .

$u_{lower} = 0$

Step 1.4

Substitute the upper limit in for $x$ in $u = 4 x$ .

$u_{upper} = 4 \frac{π}{4}$

Step 1.5

Cancel the common factor of $4$ .

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Step 1.5.1

Cancel the common factor.

$u_{upper} = 4 \frac{π}{4}$

Step 1.5.2

Rewrite the expression.

$u_{upper} = π$

Step 1.6

The values found for $u_{lower}$ and $u_{upper}$ will be used to evaluate the definite integral.

$u_{lower} = 0$

$u_{upper} = π$

Step 1.7

Rewrite the problem using $u$ , $d u$ , and the new limits of integration.

$\int_{0}^{π} \sin (u) \frac{1}{4} d u$

Step 2

Combine $\sin (u)$ and $\frac{1}{4}$ .

$\int_{0}^{π} \frac{\sin (u)}{4} d u$

Step 3

Since $\frac{1}{4}$ is constant with respect to $u$ , move $\frac{1}{4}$ out of the integral.

$\frac{1}{4} \int_{0}^{π} \sin (u) d u$

Step 4

The integral of $\sin (u)$ with respect to $u$ is $- \cos (u)$ .

$\frac{1}{4} - \cos (u)]_{0}^{π}$

Step 5

Evaluate $- \cos (u)$ at $π$ and at $0$ .

$\frac{1}{4} ((- \cos (π)) + \cos (0))$

Step 6

The exact value of $\cos (0)$ is $1$ .

$\frac{1}{4} (- \cos (π) + 1)$

Step 7

Simplify.

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Step 7.1

Apply the reference angle by finding the angle with equivalent trig values in the first quadrant. Make the expression negative because cosine is negative in the second quadrant.

$\frac{1}{4} (- - \cos (0) + 1)$

Step 7.2

The exact value of $\cos (0)$ is $1$ .

$\frac{1}{4} (- (- 1 \cdot 1) + 1)$

Step 7.3

Multiply $- 1$ by $1$ .

$\frac{1}{4} (- - 1 + 1)$

Step 7.4

Multiply $- 1$ by $- 1$ .

$\frac{1}{4} (1 + 1)$

Step 7.5

Add $1$ and $1$ .

$\frac{1}{4} \cdot 2$

Step 7.6

Cancel the common factor of $2$ .

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Step 7.6.1

Factor $2$ out of $4$ .

$\frac{1}{2 (2)} \cdot 2$

Step 7.6.2

Cancel the common factor.

$\frac{1}{2 \cdot 2} \cdot 2$

Step 7.6.3

Rewrite the expression.

$\frac{1}{2}$

Step 8

The result can be shown in multiple forms.

Exact Form:

$\frac{1}{2}$

Decimal Form:

$0.5$