- 0. Functions7h 52m
- Introduction to Functions16m
- Piecewise Functions10m
- Properties of Functions9m
- Common Functions1h 8m
- Transformations5m
- Combining Functions27m
- Exponent rules32m
- Exponential Functions28m
- Logarithmic Functions24m
- Properties of Logarithms34m
- Exponential & Logarithmic Equations35m
- Introduction to Trigonometric Functions38m
- Graphs of Trigonometric Functions44m
- Trigonometric Identities47m
- Inverse Trigonometric Functions48m
- 1. Limits and Continuity2h 2m
- 2. Intro to Derivatives1h 33m
- 3. Techniques of Differentiation3h 18m
- 4. Applications of Derivatives2h 38m
- 5. Graphical Applications of Derivatives6h 2m
- 6. Derivatives of Inverse, Exponential, & Logarithmic Functions2h 37m
- 7. Antiderivatives & Indefinite Integrals1h 26m
- 8. Definite Integrals3h 25m
4. Applications of Derivatives
Implicit Differentiation
Problem 3.85
Textbook Question
In Exercises 83–88, find equations for the lines that are tangent, and the lines that are normal, to the curve at the given point.
xy + 2x - 5y = 2, (3, 2)

1
First, we need to find the derivative of the given equation implicitly. Start with the equation: $xy + 2x - 5y = 2$. Differentiate both sides with respect to $x$. Remember to use the product rule for $xy$ and the chain rule for $-5y$.
Applying the product rule to $xy$, we get: $\frac{d}{dx}(xy) = x \frac{dy}{dx} + y$. For $2x$, the derivative is simply $2$. For $-5y$, using the chain rule, the derivative is $-5 \frac{dy}{dx}$. Set the derivative of the right side, which is a constant, to zero.
Combine all the derivatives: $x \frac{dy}{dx} + y + 2 - 5 \frac{dy}{dx} = 0$. Rearrange the terms to solve for $\frac{dy}{dx}$, which represents the slope of the tangent line.
Substitute the given point $(3, 2)$ into the equation to find the specific slope of the tangent line at that point. This will give you the value of $\frac{dy}{dx}$ at $(3, 2)$.
Once you have the slope of the tangent line, use the point-slope form of a line, $y - y_1 = m(x - x_1)$, where $m$ is the slope and $(x_1, y_1)$ is the point $(3, 2)$, to write the equation of the tangent line. For the normal line, use the negative reciprocal of the tangent slope and apply the point-slope form again.
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