Calculus Examples

$x^{2} + y^{2} = 16 x$

Step 1

Differentiate both sides of the equation.

$\frac{d}{d x} (x^{2} + y^{2}) = \frac{d}{d x} (16 x)$

Step 2

Differentiate the left side of the equation.

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Step 2.1

Differentiate.

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Step 2.1.1

By the Sum Rule, the derivative of $x^{2} + y^{2}$ with respect to $x$ is $\frac{d}{d x} [x^{2}] + \frac{d}{d x} [y^{2}]$ .

$\frac{d}{d x} [x^{2}] + \frac{d}{d x} [y^{2}]$

Step 2.1.2

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 2$ .

$2 x + \frac{d}{d x} [y^{2}]$

Step 2.2

Evaluate $\frac{d}{d x} [y^{2}]$ .

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Step 2.2.1

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

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Step 2.2.1.1

To apply the Chain Rule, set $u$ as $y$ .

$2 x + \frac{d}{d u} [u^{2}] \frac{d}{d x} [y]$

Step 2.2.1.2

Differentiate using the Power Rule which states that $\frac{d}{d u} [u^{n}]$ is $n u^{n - 1}$ where $n = 2$ .

$2 x + 2 u \frac{d}{d x} [y]$

Step 2.2.1.3

Replace all occurrences of $u$ with $y$ .

$2 x + 2 y \frac{d}{d x} [y]$

Step 2.2.2

Rewrite $\frac{d}{d x} [y]$ as $y'$ .

$2 x + 2 y y'$

Step 2.3

Reorder terms.

$2 y y' + 2 x$

Step 3

Differentiate the right side of the equation.

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Step 3.1

Since $16$ is constant with respect to $x$ , the derivative of $16 x$ with respect to $x$ is $16 \frac{d}{d x} [x]$ .

$16 \frac{d}{d x} [x]$

Step 3.2

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

$16 \cdot 1$

Step 3.3

Multiply $16$ by $1$ .

$16$

Step 4

Reform the equation by setting the left side equal to the right side.

$2 y y' + 2 x = 16$

Step 5

Solve for $y'$ .

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Step 5.1

Subtract $2 x$ from both sides of the equation.

$2 y y' = 16 - 2 x$

Step 5.2

Divide each term in $2 y y' = 16 - 2 x$ by $2 y$ and simplify.

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Step 5.2.1

Divide each term in $2 y y' = 16 - 2 x$ by $2 y$ .

$\frac{2 y y'}{2 y} = \frac{16}{2 y} + \frac{- 2 x}{2 y}$

Step 5.2.2

Simplify the left side.

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Step 5.2.2.1

Cancel the common factor of $2$ .

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Step 5.2.2.1.1

Cancel the common factor.

$\frac{2 y y'}{2 y} = \frac{16}{2 y} + \frac{- 2 x}{2 y}$

Step 5.2.2.1.2

Rewrite the expression.

$\frac{y y'}{y} = \frac{16}{2 y} + \frac{- 2 x}{2 y}$

Step 5.2.2.2

Cancel the common factor of $y$ .

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Step 5.2.2.2.1

Cancel the common factor.

$\frac{y y'}{y} = \frac{16}{2 y} + \frac{- 2 x}{2 y}$

Step 5.2.2.2.2

Divide $y'$ by $1$ .

$y' = \frac{16}{2 y} + \frac{- 2 x}{2 y}$

Step 5.2.3

Simplify the right side.

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Step 5.2.3.1

Simplify each term.

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Step 5.2.3.1.1

Cancel the common factor of $16$ and $2$ .

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Step 5.2.3.1.1.1

Factor $2$ out of $16$ .

$y' = \frac{2 \cdot 8}{2 y} + \frac{- 2 x}{2 y}$

Step 5.2.3.1.1.2

Cancel the common factors.

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Step 5.2.3.1.1.2.1

Factor $2$ out of $2 y$ .

$y' = \frac{2 \cdot 8}{2 (y)} + \frac{- 2 x}{2 y}$

Step 5.2.3.1.1.2.2

Cancel the common factor.

$y' = \frac{2 \cdot 8}{2 y} + \frac{- 2 x}{2 y}$

Step 5.2.3.1.1.2.3

Rewrite the expression.

$y' = \frac{8}{y} + \frac{- 2 x}{2 y}$

Step 5.2.3.1.2

Cancel the common factor of $- 2$ and $2$ .

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Step 5.2.3.1.2.1

Factor $2$ out of $- 2 x$ .

$y' = \frac{8}{y} + \frac{2 (- x)}{2 y}$

Step 5.2.3.1.2.2

Cancel the common factors.

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Step 5.2.3.1.2.2.1

Factor $2$ out of $2 y$ .

$y' = \frac{8}{y} + \frac{2 (- x)}{2 (y)}$

Step 5.2.3.1.2.2.2

Cancel the common factor.

$y' = \frac{8}{y} + \frac{2 (- x)}{2 y}$

Step 5.2.3.1.2.2.3

Rewrite the expression.

$y' = \frac{8}{y} + \frac{- x}{y}$

Step 5.2.3.1.3

Move the negative in front of the fraction.

$y' = \frac{8}{y} - \frac{x}{y}$

Step 6

Replace $y'$ with $\frac{d y}{d x}$ .

$\frac{d y}{d x} = \frac{8}{y} - \frac{x}{y}$

Step 7

Set $\frac{d y}{d x} = 0$ then solve for $x$ in terms of $y$ .

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Step 7.1

Subtract $\frac{8}{y}$ from both sides of the equation.

$- \frac{x}{y} = - \frac{8}{y}$

Step 7.2

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

$- x = - 8$

Step 7.3

Divide each term in $- x = - 8$ by $- 1$ and simplify.

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Step 7.3.1

Divide each term in $- x = - 8$ by $- 1$ .

$\frac{- x}{- 1} = \frac{- 8}{- 1}$

Step 7.3.2

Simplify the left side.

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Step 7.3.2.1

Dividing two negative values results in a positive value.

$\frac{x}{1} = \frac{- 8}{- 1}$

Step 7.3.2.2

Divide $x$ by $1$ .

$x = \frac{- 8}{- 1}$

Step 7.3.3

Simplify the right side.

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Step 7.3.3.1

Divide $- 8$ by $- 1$ .

$x = 8$

Step 8

Solve for $y$ .

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Step 8.1

Raise $8$ to the power of $2$ .

$64 + y^{2} = 16 (8)$

Step 8.2

Multiply $16$ by $8$ .

$64 + y^{2} = 128$

Step 8.3

Move all terms not containing $y$ to the right side of the equation.

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Step 8.3.1

Subtract $64$ from both sides of the equation.

$y^{2} = 128 - 64$

Step 8.3.2

Subtract $64$ from $128$ .

$y^{2} = 64$

Step 8.4

Take the specified root of both sides of the equation to eliminate the exponent on the left side.

$y = \pm \sqrt{64}$

Step 8.5

Simplify $\pm \sqrt{64}$ .

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Step 8.5.1

Rewrite $64$ as $8^{2}$ .

$y = \pm \sqrt{8^{2}}$

Step 8.5.2

Pull terms out from under the radical, assuming positive real numbers.

$y = \pm 8$

Step 8.6

The complete solution is the result of both the positive and negative portions of the solution.

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Step 8.6.1

First, use the positive value of the $\pm$ to find the first solution.

$y = 8$

Step 8.6.2

Next, use the negative value of the $\pm$ to find the second solution.

$y = - 8$

Step 8.6.3

The complete solution is the result of both the positive and negative portions of the solution.

$y = 8, - 8$

Step 9

Find the points where $\frac{d y}{d x} = 0$ .

$(8, 8)$

$(8, - 8)$

Step 10