Math Problem Statement

Find y' by implicit differentiation. e^{x/y} = 3x - 4y

Solution

To find yy' (the derivative of yy with respect to xx) by implicit differentiation, let's differentiate both sides of the equation with respect to xx. The equation is:

ex/y=3x4ye^{x/y} = 3x - 4y

Step 1: Differentiate the left-hand side

The derivative of ex/ye^{x/y} requires the chain rule:

ddx(ex/y)=ex/yddx(xy)\frac{d}{dx} \left( e^{x/y} \right) = e^{x/y} \cdot \frac{d}{dx} \left( \frac{x}{y} \right)

Now, use the quotient rule to differentiate xy\frac{x}{y}:

ddx(xy)=y1xyy2=yxyy2\frac{d}{dx} \left( \frac{x}{y} \right) = \frac{y \cdot 1 - x \cdot y'}{y^2} = \frac{y - x y'}{y^2}

Thus, the derivative of the left-hand side is:

ex/yyxyy2e^{x/y} \cdot \frac{y - x y'}{y^2}

Step 2: Differentiate the right-hand side

The derivative of 3x4y3x - 4y is:

ddx(3x4y)=34y\frac{d}{dx}(3x - 4y) = 3 - 4y'

Step 3: Combine the derivatives

Now, we combine the results of both sides:

ex/yyxyy2=34ye^{x/y} \cdot \frac{y - x y'}{y^2} = 3 - 4y'

Step 4: Solve for yy'

First, multiply both sides by y2y^2 to simplify:

ex/y(yxy)=y2(34y)e^{x/y} (y - x y') = y^2 (3 - 4y')

Expand both sides:

ex/yyex/yxy=3y24y2ye^{x/y} y - e^{x/y} x y' = 3y^2 - 4y^2 y'

Now, collect all the terms involving yy' on one side:

ex/yxy+4y2y=3y2ex/yy- e^{x/y} x y' + 4y^2 y' = 3y^2 - e^{x/y} y

Factor out yy':

y(ex/yx+4y2)=3y2ex/yyy'(- e^{x/y} x + 4y^2) = 3y^2 - e^{x/y} y

Finally, solve for yy':

y=3y2ex/yy4y2ex/yxy' = \frac{3y^2 - e^{x/y} y}{4y^2 - e^{x/y} x}

This is the expression for yy' found by implicit differentiation.

Would you like further clarification or details?

Follow-up questions:

  1. Can you explain the quotient rule used in this context?
  2. What is the chain rule, and how was it applied to the term ex/ye^{x/y}?
  3. Why did we factor out yy' in the final step?
  4. How do you use implicit differentiation in other types of equations?
  5. Can implicit differentiation be used for parametric equations?

Tip:

Always remember to use the chain rule when differentiating functions with variables inside an exponent!

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Math Problem Analysis

Mathematical Concepts

Implicit Differentiation
Chain Rule
Quotient Rule
Exponential Functions

Formulas

Implicit differentiation: \frac{d}{dx}f(x, y) = 0
Chain rule: \frac{d}{dx} e^{u} = e^{u} \cdot \frac{du}{dx}
Quotient rule: \frac{d}{dx}\left( \frac{f(x)}{g(x)} \right) = \frac{g(x)f'(x) - f(x)g'(x)}{g(x)^2}

Theorems

Chain Rule
Quotient Rule

Suitable Grade Level

Grades 11-12