Calculus Examples

$f (x) = \sin (\frac{x}{2})$ , $[\frac{π}{2}, \frac{3 π}{2}]$

Step 1

If $f$ is continuous on the interval $[a, b]$ and differentiable on $(a, b)$ , then at least one real number $c$ exists in the interval $(a, b)$ such that $f' (c) = \frac{f (b) - f a}{b - a}$ . The mean value theorem expresses the relationship between the slope of the tangent to the curve at $x = c$ and the slope of the line through the points $(a, f (a))$ and $(b, f (b))$ .

If $f (x)$ is continuous on $[a, b]$

and if $f (x)$ differentiable on $(a, b)$ ,

then there exists at least one point, $c$ in $[a, b]$ : $f' (c) = \frac{f (b) - f a}{b - a}$ .

Step 2

Check if $f (x) = \sin (\frac{x}{2})$ is continuous.

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Step 2.1

The domain of the expression is all real numbers except where the expression is undefined. In this case, there is no real number that makes the expression undefined.

Interval Notation:

$(- \infty, \infty)$

Set-Builder Notation:

${x | x \in ℝ}$

Step 2.2

$f (x)$ is continuous on $[\frac{π}{2}, \frac{3 π}{2}]$ .

The function is continuous.

Step 3

Find the derivative.

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Step 3.1

Find the first derivative.

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Step 3.1.1

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = \sin (x)$ and $g (x) = \frac{x}{2}$ .

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Step 3.1.1.1

To apply the Chain Rule, set $u$ as $\frac{x}{2}$ .

$\frac{d}{d u} [\sin (u)] \frac{d}{d x} [\frac{x}{2}]$

Step 3.1.1.2

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

$\cos (u) \frac{d}{d x} [\frac{x}{2}]$

Step 3.1.1.3

Replace all occurrences of $u$ with $\frac{x}{2}$ .

$\cos (\frac{x}{2}) \frac{d}{d x} [\frac{x}{2}]$

Step 3.1.2

Differentiate.

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Step 3.1.2.1

Since $\frac{1}{2}$ is constant with respect to $x$ , the derivative of $\frac{x}{2}$ with respect to $x$ is $\frac{1}{2} \frac{d}{d x} [x]$ .

$\cos (\frac{x}{2}) (\frac{1}{2} \frac{d}{d x} [x])$

Step 3.1.2.2

Combine $\frac{1}{2}$ and $\cos (\frac{x}{2})$ .

$\frac{\cos (\frac{x}{2})}{2} \frac{d}{d x} [x]$

Step 3.1.2.3

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

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

Step 3.1.2.4

Multiply $\frac{\cos (\frac{x}{2})}{2}$ by $1$ .

$f' (x) = \frac{\cos (\frac{x}{2})}{2}$

Step 3.2

The first derivative of $f (x)$ with respect to $x$ is $\frac{\cos (\frac{x}{2})}{2}$ .

$\frac{\cos (\frac{x}{2})}{2}$

Step 4

Find if the derivative is continuous on $(\frac{π}{2}, \frac{3 π}{2})$ .

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Step 4.1

The domain of the expression is all real numbers except where the expression is undefined. In this case, there is no real number that makes the expression undefined.

Interval Notation:

$(- \infty, \infty)$

Set-Builder Notation:

${x | x \in ℝ}$

Step 4.2

$f' (x)$ is continuous on $(\frac{π}{2}, \frac{3 π}{2})$ .

The function is continuous.

Step 5

The function is differentiable on $(\frac{π}{2}, \frac{3 π}{2})$ because the derivative is continuous on $(\frac{π}{2}, \frac{3 π}{2})$ .

The function is differentiable.

Step 6

$f (x)$ satisfies the two conditions for the mean value theorem. It is continuous on $[\frac{π}{2}, \frac{3 π}{2}]$ and differentiable on $(\frac{π}{2}, \frac{3 π}{2})$ .

$f (x)$ is continuous on $[\frac{π}{2}, \frac{3 π}{2}]$ and differentiable on $(\frac{π}{2}, \frac{3 π}{2})$ .

Step 7

Evaluate $f (a)$ from the interval $[\frac{π}{2}, \frac{3 π}{2}]$ .

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Step 7.1

Replace the variable $x$ with $\frac{π}{2}$ in the expression.

$f (\frac{π}{2}) = \sin (\frac{\frac{π}{2}}{2})$

Step 7.2

Simplify the result.

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Step 7.2.1

Multiply the numerator by the reciprocal of the denominator.

$f (\frac{π}{2}) = \sin (\frac{π}{2} \cdot \frac{1}{2})$

Step 7.2.2

Multiply $\frac{π}{2} \cdot \frac{1}{2}$ .

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Step 7.2.2.1

Multiply $\frac{π}{2}$ by $\frac{1}{2}$ .

$f (\frac{π}{2}) = \sin (\frac{π}{2 \cdot 2})$

Step 7.2.2.2

Multiply $2$ by $2$ .

$f (\frac{π}{2}) = \sin (\frac{π}{4})$

Step 7.2.3

The exact value of $\sin (\frac{π}{4})$ is $\frac{\sqrt{2}}{2}$ .

$f (\frac{π}{2}) = \frac{\sqrt{2}}{2}$

Step 7.2.4

The final answer is $\frac{\sqrt{2}}{2}$ .

$\frac{\sqrt{2}}{2}$

Step 8

Solve $\frac{\cos (\frac{x}{2})}{2} = \frac{- (f (b) + f (a))}{- (b + a)}$ for $x$ . $\frac{\cos (\frac{x}{2})}{2} = \frac{- (f (\frac{3 π}{2}) + f (\frac{π}{2}))}{- (\frac{3 π}{2} + \frac{π}{2})}$ .

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Step 8.1

Multiply both sides of the equation by $2$ .

$2 \frac{\cos (\frac{x}{2})}{2} = 2 \frac{\frac{\sqrt{2}}{2} - \frac{\sqrt{2}}{2}}{\frac{3 π}{2} - \frac{π}{2}}$

Step 8.2

Simplify both sides of the equation.

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Step 8.2.1

Simplify the left side.

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Step 8.2.1.1

Cancel the common factor of $2$ .

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Step 8.2.1.1.1

Cancel the common factor.

$2 \frac{\cos (\frac{x}{2})}{2} = 2 \frac{\frac{\sqrt{2}}{2} - \frac{\sqrt{2}}{2}}{\frac{3 π}{2} - \frac{π}{2}}$

Step 8.2.1.1.2

Rewrite the expression.

$\cos (\frac{x}{2}) = 2 \frac{\frac{\sqrt{2}}{2} - \frac{\sqrt{2}}{2}}{\frac{3 π}{2} - \frac{π}{2}}$

Step 8.2.2

Simplify the right side.

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Step 8.2.2.1

Simplify $2 \frac{\frac{\sqrt{2}}{2} - \frac{\sqrt{2}}{2}}{\frac{3 π}{2} - \frac{π}{2}}$ .

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Step 8.2.2.1.1

Multiply the numerator and denominator of the fraction by $2$ .

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Step 8.2.2.1.1.1

Multiply $\frac{\frac{\sqrt{2}}{2} - \frac{\sqrt{2}}{2}}{\frac{3 π}{2} - \frac{π}{2}}$ by $\frac{2}{2}$ .

$\cos (\frac{x}{2}) = 2 (\frac{2}{2} \cdot \frac{\frac{\sqrt{2}}{2} - \frac{\sqrt{2}}{2}}{\frac{3 π}{2} - \frac{π}{2}})$

Step 8.2.2.1.1.2

Combine.

$\cos (\frac{x}{2}) = 2 \frac{2 (\frac{\sqrt{2}}{2} - \frac{\sqrt{2}}{2})}{2 (\frac{3 π}{2} - \frac{π}{2})}$

Step 8.2.2.1.2

Apply the distributive property.

$\cos (\frac{x}{2}) = 2 \frac{2 \frac{\sqrt{2}}{2} + 2 (- \frac{\sqrt{2}}{2})}{2 \frac{3 π}{2} + 2 (- \frac{π}{2})}$

Step 8.2.2.1.3

Simplify by cancelling.

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Step 8.2.2.1.3.1

Cancel the common factor of $2$ .

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Step 8.2.2.1.3.1.1

Cancel the common factor.

$\cos (\frac{x}{2}) = 2 \frac{2 \frac{\sqrt{2}}{2} + 2 (- \frac{\sqrt{2}}{2})}{2 \frac{3 π}{2} + 2 (- \frac{π}{2})}$

Step 8.2.2.1.3.1.2

Rewrite the expression.

$\cos (\frac{x}{2}) = 2 \frac{\sqrt{2} + 2 (- \frac{\sqrt{2}}{2})}{2 \frac{3 π}{2} + 2 (- \frac{π}{2})}$

Step 8.2.2.1.3.2

Cancel the common factor of $2$ .

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Step 8.2.2.1.3.2.1

Move the leading negative in $- \frac{\sqrt{2}}{2}$ into the numerator.

$\cos (\frac{x}{2}) = 2 \frac{\sqrt{2} + 2 \frac{- \sqrt{2}}{2}}{2 \frac{3 π}{2} + 2 (- \frac{π}{2})}$

Step 8.2.2.1.3.2.2

Cancel the common factor.

$\cos (\frac{x}{2}) = 2 \frac{\sqrt{2} + 2 \frac{- \sqrt{2}}{2}}{2 \frac{3 π}{2} + 2 (- \frac{π}{2})}$

Step 8.2.2.1.3.2.3

Rewrite the expression.

$\cos (\frac{x}{2}) = 2 \frac{\sqrt{2} - \sqrt{2}}{2 \frac{3 π}{2} + 2 (- \frac{π}{2})}$

Step 8.2.2.1.3.3

Cancel the common factor of $2$ .

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Step 8.2.2.1.3.3.1

Cancel the common factor.

$\cos (\frac{x}{2}) = 2 \frac{\sqrt{2} - \sqrt{2}}{2 \frac{3 π}{2} + 2 (- \frac{π}{2})}$

Step 8.2.2.1.3.3.2

Rewrite the expression.

$\cos (\frac{x}{2}) = 2 \frac{\sqrt{2} - \sqrt{2}}{3 π + 2 (- \frac{π}{2})}$

Step 8.2.2.1.3.4

Cancel the common factor of $2$ .

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Step 8.2.2.1.3.4.1

Move the leading negative in $- \frac{π}{2}$ into the numerator.

$\cos (\frac{x}{2}) = 2 \frac{\sqrt{2} - \sqrt{2}}{3 π + 2 \frac{- π}{2}}$

Step 8.2.2.1.3.4.2

Cancel the common factor.

$\cos (\frac{x}{2}) = 2 \frac{\sqrt{2} - \sqrt{2}}{3 π + 2 \frac{- π}{2}}$

Step 8.2.2.1.3.4.3

Rewrite the expression.

$\cos (\frac{x}{2}) = 2 \frac{\sqrt{2} - \sqrt{2}}{3 π - π}$

Step 8.2.2.1.4

Simplify terms.

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Step 8.2.2.1.4.1

Subtract $\sqrt{2}$ from $\sqrt{2}$ .

$\cos (\frac{x}{2}) = 2 \frac{0}{3 π - π}$

Step 8.2.2.1.4.2

Subtract $π$ from $3 π$ .

$\cos (\frac{x}{2}) = 2 \frac{0}{2 π}$

Step 8.2.2.1.4.3

Cancel the common factor of $2$ .

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Step 8.2.2.1.4.3.1

Factor $2$ out of $2 π$ .

$\cos (\frac{x}{2}) = 2 \frac{0}{2 (π)}$

Step 8.2.2.1.4.3.2

Cancel the common factor.

$\cos (\frac{x}{2}) = 2 \frac{0}{2 π}$

Step 8.2.2.1.4.3.3

Rewrite the expression.

$\cos (\frac{x}{2}) = \frac{0}{π}$

Step 8.2.2.1.4.4

Divide $0$ by $π$ .

$\cos (\frac{x}{2}) = 0$

Step 8.3

Take the inverse cosine of both sides of the equation to extract $x$ from inside the cosine.

$\frac{x}{2} = \arccos (0)$

Step 8.4

Simplify the right side.

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Step 8.4.1

The exact value of $\arccos (0)$ is $\frac{π}{2}$ .

$\frac{x}{2} = \frac{π}{2}$

Step 8.5

Since the expression on each side of the equation has the same denominator, the numerators must be equal.

$x = π$

Step 8.6

The cosine function is positive in the first and fourth quadrants. To find the second solution, subtract the reference angle from $2 π$ to find the solution in the fourth quadrant.

$\frac{x}{2} = 2 π - \frac{π}{2}$

Step 8.7

Solve for $x$ .

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Step 8.7.1

Multiply both sides of the equation by $2$ .

$2 \frac{x}{2} = 2 (2 π - \frac{π}{2})$

Step 8.7.2

Simplify both sides of the equation.

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Step 8.7.2.1

Simplify the left side.

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Step 8.7.2.1.1

Cancel the common factor of $2$ .

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Step 8.7.2.1.1.1

Cancel the common factor.

$2 \frac{x}{2} = 2 (2 π - \frac{π}{2})$

Step 8.7.2.1.1.2

Rewrite the expression.

$x = 2 (2 π - \frac{π}{2})$

Step 8.7.2.2

Simplify the right side.

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Step 8.7.2.2.1

Simplify $2 (2 π - \frac{π}{2})$ .

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Step 8.7.2.2.1.1

To write $2 π$ as a fraction with a common denominator, multiply by $\frac{2}{2}$ .

$x = 2 (2 π \cdot \frac{2}{2} - \frac{π}{2})$

Step 8.7.2.2.1.2

Combine $2 π$ and $\frac{2}{2}$ .

$x = 2 (\frac{2 π \cdot 2}{2} - \frac{π}{2})$

Step 8.7.2.2.1.3

Combine the numerators over the common denominator.

$x = 2 \frac{2 π \cdot 2 - π}{2}$

Step 8.7.2.2.1.4

Cancel the common factor of $2$ .

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Step 8.7.2.2.1.4.1

Cancel the common factor.

$x = 2 \frac{2 π \cdot 2 - π}{2}$

Step 8.7.2.2.1.4.2

Rewrite the expression.

$x = 2 π \cdot 2 - π$

Step 8.7.2.2.1.5

Multiply $2$ by $2$ .

$x = 4 π - π$

Step 8.7.2.2.1.6

Subtract $π$ from $4 π$ .

$x = 3 π$

Step 8.8

Find the period of $\cos (\frac{x}{2})$ .

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Step 8.8.1

The period of the function can be calculated using $\frac{2 π}{| b |}$ .

$\frac{2 π}{| b |}$

Step 8.8.2

Replace $b$ with $\frac{1}{2}$ in the formula for period.

$\frac{2 π}{| \frac{1}{2} |}$

Step 8.8.3

$\frac{1}{2}$ is approximately $0.5$ which is positive so remove the absolute value

$\frac{2 π}{\frac{1}{2}}$

Step 8.8.4

Multiply the numerator by the reciprocal of the denominator.

$2 π \cdot 2$

Step 8.8.5

Multiply $2$ by $2$ .

$4 π$

Step 8.9

The period of the $\cos (\frac{x}{2})$ function is $4 π$ so values will repeat every $4 π$ radians in both directions.

$x = π + 4 π n, 3 π + 4 π n$ , for any integer $n$

Step 8.10

Consolidate the answers.

$x = π + 2 π n$ , for any integer $n$

Step 9

There is a tangent line found at $x = π + 2 π n$ parallel to the line that passes through the end points $a = \frac{π}{2}$ and $b = \frac{3 π}{2}$ .

There is a tangent line at $x = π + 2 π n$ parallel to the line that passes through the end points $a = \frac{π}{2}$ and $b = \frac{3 π}{2}$

Step 10