Math Problem Statement

If -4x^2 + 3y^2 + 4y = 0, then find d^2y/dx^2 at the point (1, -2) in simplest form.

Solution

The problem asks you to find the second derivative, d2ydx2\frac{d^2y}{dx^2}, implicitly using the equation:

4x2+3y2+4y=0-4x^2 + 3y^2 + 4y = 0

at the point (1,2)(1, -2).

Steps:

  1. Differentiate the given equation implicitly with respect to xx:

    ddx(4x2+3y2+4y)=0\frac{d}{dx} \left( -4x^2 + 3y^2 + 4y \right) = 0

    Apply the chain rule to differentiate y2y^2 and yy terms:

    8x+6ydydx+4dydx=0-8x + 6y \frac{dy}{dx} + 4 \frac{dy}{dx} = 0

    Combine terms:

    8x+(6y+4)dydx=0-8x + (6y + 4) \frac{dy}{dx} = 0

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

    dydx=8x6y+4\frac{dy}{dx} = \frac{8x}{6y + 4}

    At the point (1,2)(1, -2):

    dydx=8(1)6(2)+4=812+4=88=1\frac{dy}{dx} = \frac{8(1)}{6(-2) + 4} = \frac{8}{-12 + 4} = \frac{8}{-8} = -1

  3. Differentiate implicitly again to find the second derivative d2ydx2\frac{d^2y}{dx^2}:

    Differentiate dydx=8x6y+4\frac{dy}{dx} = \frac{8x}{6y + 4} again with respect to xx, applying the quotient rule:

    ddx(8x6y+4)\frac{d}{dx} \left( \frac{8x}{6y + 4} \right)

    Apply the quotient rule ddx(uv)=vdudxudvdxv2\frac{d}{dx} \left( \frac{u}{v} \right) = \frac{v \frac{du}{dx} - u \frac{dv}{dx}}{v^2}, where u=8xu = 8x and v=6y+4v = 6y + 4:

    d2ydx2=(6y+4)(8)8x(6dydx)(6y+4)2\frac{d^2y}{dx^2} = \frac{(6y + 4)(8) - 8x(6 \frac{dy}{dx})}{(6y + 4)^2}

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

    d2ydx2=(12+4)(8)8(1)(6)(1)(12+4)2\frac{d^2y}{dx^2} = \frac{(-12 + 4)(8) - 8(1)(6)(-1)}{(-12 + 4)^2}

    Simplify the numerator:

    (8)(8)8(6)(1)=64+48=16(-8)(8) - 8(6)(-1) = -64 + 48 = -16

    And the denominator:

    (8)2=64(-8)^2 = 64

    Thus:

    d2ydx2=1664=14\frac{d^2y}{dx^2} = \frac{-16}{64} = -\frac{1}{4}

Final Answer:

d2ydx2=14\frac{d^2y}{dx^2} = -\frac{1}{4}

Would you like any additional details or explanations?


Here are 5 related questions you might find helpful:

  1. How do you apply the quotient rule in implicit differentiation?
  2. Why do we need to differentiate twice to find the second derivative?
  3. Can implicit differentiation always be used to find higher-order derivatives?
  4. How does the chain rule affect the differentiation of y2y^2?
  5. What would change if the point was (1,2)(1, 2) instead of (1,2)(1, -2)?

Tip: Always check your first derivative before proceeding to the second derivative in implicit differentiation!

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Math Problem Analysis

Mathematical Concepts

Implicit Differentiation
Second Derivative
Quotient Rule
Chain Rule

Formulas

Implicit differentiation of -4x^2 + 3y^2 + 4y = 0
First derivative: dy/dx = 8x / (6y + 4)
Second derivative using quotient rule: d^2y/dx^2 = (v(du/dx) - u(dv/dx)) / v^2

Theorems

Quotient Rule
Chain Rule
Implicit Differentiation

Suitable Grade Level

College Calculus