Math Problem Statement

Using implicit differentiation, (Second Derivative), If -2x^3 + y - y^2 = 0 then find the second derivative at the point (-1,2) in simplest form. Derivate with respect to x, use chain rule for y terms, rearrange terms with y prime on the left, other terms on the right, then divide, simplify any common factors, convert y prime to dy/dx, then find the 2nd derivative using the product or quotient rule, then plug in y, y prime, and x

Solution

To find the second derivative of the implicit function 2x3+yy2=0-2x^3 + y - y^2 = 0 at the point (1,2)(-1, 2), we will follow the steps outlined:

Step 1: First Derivative using Implicit Differentiation

  1. Differentiate both sides of the equation with respect to xx:

    ddx(2x3)+ddx(y)ddx(y2)=0\frac{d}{dx}(-2x^3) + \frac{d}{dx}(y) - \frac{d}{dx}(y^2) = 0

    This gives:

    6x2+dydx2ydydx=0-6x^2 + \frac{dy}{dx} - 2y \frac{dy}{dx} = 0

  2. Rearrange the equation to isolate dydx\frac{dy}{dx}:

    dydx(12y)=6x2\frac{dy}{dx}(1 - 2y) = 6x^2

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

    dydx=6x212y\frac{dy}{dx} = \frac{6x^2}{1 - 2y}

Step 2: Evaluate the First Derivative at the Point (1,2)(-1, 2)

Plugging in x=1x = -1 and y=2y = 2:

dydx=6(1)212(2)=614=63=2\frac{dy}{dx} = \frac{6(-1)^2}{1 - 2(2)} = \frac{6}{1 - 4} = \frac{6}{-3} = -2

Step 3: Second Derivative

  1. Differentiate dydx=6x212y\frac{dy}{dx} = \frac{6x^2}{1 - 2y} again with respect to xx:

    Using the quotient rule:

    d2ydx2=(12y)ddx(6x2)6x2ddx(12y)(12y)2\frac{d^2y}{dx^2} = \frac{(1 - 2y)\frac{d}{dx}(6x^2) - 6x^2\frac{d}{dx}(1 - 2y)}{(1 - 2y)^2}

    Calculating each part:

    • ddx(6x2)=12x\frac{d}{dx}(6x^2) = 12x
    • ddx(12y)=2dydx\frac{d}{dx}(1 - 2y) = -2\frac{dy}{dx}

    Substitute:

    d2ydx2=(12y)(12x)6x2(2dydx)(12y)2\frac{d^2y}{dx^2} = \frac{(1 - 2y)(12x) - 6x^2(-2\frac{dy}{dx})}{(1 - 2y)^2}

  2. Substitute x=1x = -1, y=2y = 2, and dydx=2\frac{dy}{dx} = -2:

    Calculate 12(2)=14=31 - 2(2) = 1 - 4 = -3:

    d2ydx2=(3)(12(1))6(1)2(2)(3)2\frac{d^2y}{dx^2} = \frac{(-3)(12(-1)) - 6(-1)^2(-2)}{(-3)^2}

    This simplifies to:

    d2ydx2=36129=249=83\frac{d^2y}{dx^2} = \frac{36 - 12}{9} = \frac{24}{9} = \frac{8}{3}

Final Result

The second derivative at the point (1,2)(-1, 2) is

d2ydx2=83.\frac{d^2y}{dx^2} = \frac{8}{3}.

Summary

  1. The first derivative dydx\frac{dy}{dx} at the point (1,2)(-1, 2) is 2-2.
  2. The second derivative d2ydx2\frac{d^2y}{dx^2} at the point (1,2)(-1, 2) is 83\frac{8}{3}.

Would you like to go into more detail on any of these steps or have any other questions? Here are some related questions:

  1. What is the geometric interpretation of the first derivative?
  2. How does the second derivative relate to the concavity of the function?
  3. Can you provide examples of other implicit functions and their derivatives?
  4. What is the importance of the chain rule in implicit differentiation?
  5. How would the second derivative change if the equation were different?

Tip: Always double-check your algebra when working with derivatives, as small errors can lead to incorrect results.

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Math Problem Analysis

Mathematical Concepts

Implicit Differentiation
Second Derivative
Chain Rule
Quotient Rule

Formulas

dy/dx = 6x^2 / (1 - 2y)
d^2y/dx^2 = [(1 - 2y)(12x) - 6x^2(-2 * dy/dx)] / (1 - 2y)^2

Theorems

Implicit Function Theorem
Quotient Rule

Suitable Grade Level

Grades 11-12