Calculus Examples

$x y - x^{3} = 2 y^{3}$

Step 1

Differentiate both sides of the equation.

$\frac{d}{d x} (x y - x^{3}) = \frac{d}{d x} (2 y^{3})$

Step 2

Differentiate the left side of the equation.

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Step 2.1

By the Sum Rule, the derivative of $x y - x^{3}$ with respect to $x$ is $\frac{d}{d x} [x y] + \frac{d}{d x} [- x^{3}]$ .

$\frac{d}{d x} [x y] + \frac{d}{d x} [- x^{3}]$

Step 2.2

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

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Step 2.2.1

Differentiate using the Product Rule which states that $\frac{d}{d x} [f (x) g (x)]$ is $f (x) \frac{d}{d x} [g (x)] + g (x) \frac{d}{d x} [f (x)]$ where $f (x) = x$ and $g (x) = y$ .

$x \frac{d}{d x} [y] + y \frac{d}{d x} [x] + \frac{d}{d x} [- x^{3}]$

Step 2.2.2

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

$x y' + y \frac{d}{d x} [x] + \frac{d}{d x} [- x^{3}]$

Step 2.2.3

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

$x y' + y \cdot 1 + \frac{d}{d x} [- x^{3}]$

Step 2.2.4

Multiply $y$ by $1$ .

$x y' + y + \frac{d}{d x} [- x^{3}]$

Step 2.3

Evaluate $\frac{d}{d x} [- x^{3}]$ .

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Step 2.3.1

Since $- 1$ is constant with respect to $x$ , the derivative of $- x^{3}$ with respect to $x$ is $- \frac{d}{d x} [x^{3}]$ .

$x y' + y - \frac{d}{d x} [x^{3}]$

Step 2.3.2

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 3$ .

$x y' + y - (3 x^{2})$

Step 2.3.3

Multiply $3$ by $- 1$ .

$x y' + y - 3 x^{2}$

Step 2.4

Reorder terms.

$- 3 x^{2} + x y' + y$

Step 3

Differentiate the right side of the equation.

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Step 3.1

Since $2$ is constant with respect to $x$ , the derivative of $2 y^{3}$ with respect to $x$ is $2 \frac{d}{d x} [y^{3}]$ .

$2 \frac{d}{d x} [y^{3}]$

Step 3.2

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = x^{3}$ and $g (x) = y$ .

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Step 3.2.1

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

$2 (\frac{d}{d u} [u^{3}] \frac{d}{d x} [y])$

Step 3.2.2

Differentiate using the Power Rule which states that $\frac{d}{d u} [u^{n}]$ is $n u^{n - 1}$ where $n = 3$ .

$2 (3 u^{2} \frac{d}{d x} [y])$

Step 3.2.3

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

$2 (3 y^{2} \frac{d}{d x} [y])$

Step 3.3

Multiply $3$ by $2$ .

$6 (y^{2} \frac{d}{d x} [y])$

Step 3.4

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

$6 y^{2} y'$

Step 4

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

$- 3 x^{2} + x y' + y = 6 y^{2} y'$

Step 5

Solve for $y'$ .

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Step 5.1

Subtract $6 y^{2} y'$ from both sides of the equation.

$- 3 x^{2} + x y' + y - 6 y^{2} y' = 0$

Step 5.2

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

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Step 5.2.1

Add $3 x^{2}$ to both sides of the equation.

$x y' + y - 6 y^{2} y' = 3 x^{2}$

Step 5.2.2

Subtract $y$ from both sides of the equation.

$x y' - 6 y^{2} y' = 3 x^{2} - y$

Step 5.3

Factor $y'$ out of $x y' - 6 y^{2} y'$ .

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Step 5.3.1

Factor $y'$ out of $x y'$ .

$y' x - 6 y^{2} y' = 3 x^{2} - y$

Step 5.3.2

Factor $y'$ out of $- 6 y^{2} y'$ .

$y' (x) + y' (- 6 y^{2}) = 3 x^{2} - y$

Step 5.3.3

Factor $y'$ out of $y' (x) + y' (- 6 y^{2})$ .

$y' (x - 6 y^{2}) = 3 x^{2} - y$

Step 5.4

Divide each term in $y' (x - 6 y^{2}) = 3 x^{2} - y$ by $x - 6 y^{2}$ and simplify.

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Step 5.4.1

Divide each term in $y' (x - 6 y^{2}) = 3 x^{2} - y$ by $x - 6 y^{2}$ .

$\frac{y' (x - 6 y^{2})}{x - 6 y^{2}} = \frac{3 x^{2}}{x - 6 y^{2}} + \frac{- y}{x - 6 y^{2}}$

Step 5.4.2

Simplify the left side.

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Step 5.4.2.1

Cancel the common factor of $x - 6 y^{2}$ .

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Step 5.4.2.1.1

Cancel the common factor.

$\frac{y' (x - 6 y^{2})}{x - 6 y^{2}} = \frac{3 x^{2}}{x - 6 y^{2}} + \frac{- y}{x - 6 y^{2}}$

Step 5.4.2.1.2

Divide $y'$ by $1$ .

$y' = \frac{3 x^{2}}{x - 6 y^{2}} + \frac{- y}{x - 6 y^{2}}$

Step 5.4.3

Simplify the right side.

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Step 5.4.3.1

Combine the numerators over the common denominator.

$y' = \frac{3 x^{2} - y}{x - 6 y^{2}}$

Step 6

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

$\frac{d y}{d x} = \frac{3 x^{2} - y}{x - 6 y^{2}}$