Math Problem Statement

solve

If -y^3 + x^3 + x^2 = -3y - 2y^2, then find dy/dx at the point (-1, 3).

Solution

To solve this problem, we need to implicitly differentiate the given equation with respect to xx and then solve for dydx\frac{dy}{dx}.

The given equation is:

y3+x3+x2=3y2y2-y^3 + x^3 + x^2 = -3y - 2y^2

Step 1: Implicit Differentiation

We'll differentiate both sides of the equation with respect to xx, remembering that yy is a function of xx, so we must use the chain rule when differentiating terms involving yy.

Left-hand side:

  • The derivative of y3-y^3 with respect to xx is: 3y2dydx-3y^2 \frac{dy}{dx} (by the chain rule).
  • The derivative of x3x^3 with respect to xx is: 3x23x^2
  • The derivative of x2x^2 with respect to xx is: 2x2x

So, the derivative of the left-hand side is: 3y2dydx+3x2+2x-3y^2 \frac{dy}{dx} + 3x^2 + 2x

Right-hand side:

  • The derivative of 3y-3y with respect to xx is: 3dydx-3 \frac{dy}{dx} (using the chain rule).
  • The derivative of 2y2-2y^2 with respect to xx is: 4ydydx-4y \frac{dy}{dx} (using the chain rule).

So, the derivative of the right-hand side is: 3dydx4ydydx-3 \frac{dy}{dx} - 4y \frac{dy}{dx}

Step 2: Setting up the equation

Now, we equate the derivatives of both sides:

3y2dydx+3x2+2x=3dydx4ydydx-3y^2 \frac{dy}{dx} + 3x^2 + 2x = -3 \frac{dy}{dx} - 4y \frac{dy}{dx}

Step 3: Solving for dydx\frac{dy}{dx}

We'll gather all terms involving dydx\frac{dy}{dx} on one side:

3y2dydx+3dydx+4ydydx=3x2+2x-3y^2 \frac{dy}{dx} + 3 \frac{dy}{dx} + 4y \frac{dy}{dx} = 3x^2 + 2x

Factor out dydx\frac{dy}{dx}:

dydx(3y2+3+4y)=3x2+2x\frac{dy}{dx} (-3y^2 + 3 + 4y) = 3x^2 + 2x

Solve for dydx\frac{dy}{dx}:

dydx=3x2+2x3+4y3y2\frac{dy}{dx} = \frac{3x^2 + 2x}{3 + 4y - 3y^2}

Step 4: Evaluate at the point (1,3)(-1, 3)

Now substitute x=1x = -1 and y=3y = 3 into the expression for dydx\frac{dy}{dx}:

  • For the numerator: 3(1)2+2(1)=3(1)2=13(-1)^2 + 2(-1) = 3(1) - 2 = 1

  • For the denominator: 3+4(3)3(3)2=3+1227=123 + 4(3) - 3(3)^2 = 3 + 12 - 27 = -12

Thus:

dydx=112=112\frac{dy}{dx} = \frac{1}{-12} = -\frac{1}{12}

Final Answer:

dydx=112 at the point (1,3)\frac{dy}{dx} = -\frac{1}{12} \text{ at the point } (-1, 3)

Would you like more details or have any questions? Here are some related questions to explore:

  1. What is implicit differentiation, and why do we use it?
  2. How does the chain rule apply in implicit differentiation?
  3. What are some examples where implicit differentiation is necessary?
  4. Can you differentiate a different equation implicitly and solve for dydx\frac{dy}{dx}?
  5. How would the answer change if the equation had additional terms?

Tip: Always keep track of where you apply the chain rule when differentiating implicitly!

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Math Problem Analysis

Mathematical Concepts

Implicit Differentiation
Chain Rule
Derivatives

Formulas

Implicit differentiation: d/dx[f(x, y) = g(x, y)]
Chain rule: d/dx[y^n] = n*y^(n-1) * dy/dx

Theorems

Implicit Differentiation
Chain Rule

Suitable Grade Level

Grades 11-12 (Calculus)