Math Problem Statement

Use implicit differentiation to find y' and evaluate y' at (-1,1) for the equation x ln(y) + 5y = 2x^3.

Solution

Let's solve the problem using implicit differentiation.

The given equation is:

xln(y)+5y=2x3x \ln(y) + 5y = 2x^3

Step 1: Differentiate both sides with respect to xx.

We will use the product rule, chain rule, and implicit differentiation.

Left side:

  1. ddx(xln(y))=ln(y)+x1yy\frac{d}{dx} \left( x \ln(y) \right) = \ln(y) + x \cdot \frac{1}{y} \cdot y' (product rule and chain rule for ln(y)\ln(y)).

  2. ddx(5y)=5y\frac{d}{dx} \left( 5y \right) = 5y'.

Right side:

  1. ddx(2x3)=6x2\frac{d}{dx} \left( 2x^3 \right) = 6x^2.

Thus, after differentiation: ln(y)+xyy+5y=6x2\ln(y) + \frac{x}{y} \cdot y' + 5y' = 6x^2

Step 2: Solve for yy'.

Rearranging the terms to isolate yy':

xyy+5y=6x2ln(y)\frac{x}{y} \cdot y' + 5y' = 6x^2 - \ln(y)

Factor out yy':

y(xy+5)=6x2ln(y)y' \left( \frac{x}{y} + 5 \right) = 6x^2 - \ln(y)

Now, solve for yy':

y=6x2ln(y)xy+5y' = \frac{6x^2 - \ln(y)}{\frac{x}{y} + 5}

Step 3: Evaluate yy' at (1,1)(-1, 1).

Substitute x=1x = -1 and y=1y = 1:

y=6(1)2ln(1)11+5y' = \frac{6(-1)^2 - \ln(1)}{\frac{-1}{1} + 5}

Since ln(1)=0\ln(1) = 0, the equation simplifies to:

y=6(1)01+5=64=32y' = \frac{6(1) - 0}{-1 + 5} = \frac{6}{4} = \frac{3}{2}

Final Answers:

  • y=6x2ln(y)xy+5y' = \frac{6x^2 - \ln(y)}{\frac{x}{y} + 5}
  • y(1,1)=32y'(-1, 1) = \frac{3}{2}

Would you like more details or have any questions?

Here are 5 related questions for further practice:

  1. What is implicit differentiation, and how does it differ from explicit differentiation?
  2. How does the chain rule apply when differentiating ln(y)\ln(y)?
  3. What is the product rule, and how is it applied in this problem?
  4. How would the solution change if the equation involved ln(x)\ln(x) instead of ln(y)\ln(y)?
  5. How can implicit differentiation be used in solving related rates problems?

Tip: Always simplify logarithmic terms like ln(1)=0\ln(1) = 0 early to make the differentiation process easier.

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Math Problem Analysis

Mathematical Concepts

Implicit Differentiation
Logarithmic Differentiation
Chain Rule
Product Rule

Formulas

Product rule: (fg)' = f'g + fg'
Chain rule: (ln(y))' = (1/y) * dy/dx

Theorems

Chain Rule
Product Rule

Suitable Grade Level

Grades 11-12