Math Problem Statement

If y^2 + xy - 3x = 17, and dy/dt = 3 when x = 1 and y = -5, what is dx/dt when x = 1 and y = -5?

Solution

We are given the equation y2+xy3x=17y^2 + xy - 3x = 17, along with information that dydt=3\frac{dy}{dt} = 3 when x=1x = 1 and y=5y = -5. The task is to find dxdt\frac{dx}{dt} under these same conditions.

Step-by-Step Process:

  1. Differentiate both sides of the equation with respect to tt: ddt(y2+xy3x)=ddt(17)\frac{d}{dt}(y^2 + xy - 3x) = \frac{d}{dt}(17) Using the chain rule and product rule, we get: 2ydydt+(xdydt+ydxdt)3dxdt=02y \frac{dy}{dt} + \left( x \frac{dy}{dt} + y \frac{dx}{dt} \right) - 3 \frac{dx}{dt} = 0 Simplifying, this becomes: 2ydydt+xdydt+ydxdt3dxdt=02y \frac{dy}{dt} + x \frac{dy}{dt} + y \frac{dx}{dt} - 3 \frac{dx}{dt} = 0

  2. Substitute the given values: We are given x=1x = 1, y=5y = -5, and dydt=3\frac{dy}{dt} = 3. Substituting these into the differentiated equation: 2(5)(3)+(1)(3)+(5)dxdt3dxdt=02(-5)(3) + (1)(3) + (-5) \frac{dx}{dt} - 3 \frac{dx}{dt} = 0 Simplifying the constants: 30+35dxdt3dxdt=0-30 + 3 - 5 \frac{dx}{dt} - 3 \frac{dx}{dt} = 0 This simplifies to: 278dxdt=0-27 - 8 \frac{dx}{dt} = 0

  3. Solve for dxdt\frac{dx}{dt}: 8dxdt=27-8 \frac{dx}{dt} = 27 dxdt=278\frac{dx}{dt} = -\frac{27}{8}

Thus, the value of dxdt\frac{dx}{dt} is 278-\frac{27}{8}.

Would you like more details on any of the steps or have any further questions?

Related Questions:

  1. How does the product rule apply when differentiating terms like xyxy?
  2. What does it mean physically if dxdt\frac{dx}{dt} is negative?
  3. How can you verify if the differentiation was done correctly in this problem?
  4. How would this problem change if dydt\frac{dy}{dt} were a different value?
  5. Could you solve this problem using implicit differentiation?

Tip:

When solving related rates problems, always ensure that every variable dependent on time is differentiated with respect to time, using the chain rule!

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Math Problem Analysis

Mathematical Concepts

Implicit Differentiation
Related Rates
Algebraic Equations

Formulas

Chain Rule
Product Rule

Theorems

Implicit Differentiation
Chain Rule

Suitable Grade Level

Grade 12 / Early College Calculus