Math Problem Statement

Consider the following: 8x^2 - y^5 = 9. (a) Find y' by implicit differentiation. (b) Solve the equation explicitly for y and differentiate to get y' in terms of x. (c) Check that your solutions to parts (a) and (b) are consistent by substituting the expression for y into your solution for part (a).

Solution

Let's work through this problem step by step.

The equation given is:

8x2y5=98x^2 - y^5 = 9

(a) Find yy' by implicit differentiation.

  1. Differentiate both sides of the equation with respect to xx. For the left-hand side:
    • The derivative of 8x28x^2 with respect to xx is 16x16x.
    • The derivative of y5y^5 with respect to xx is 5y4dydx5y^4 \cdot \frac{dy}{dx} (since yy is a function of xx).

So the equation becomes:

16x5y4dydx=016x - 5y^4 \cdot \frac{dy}{dx} = 0

  1. Now solve for dydx\frac{dy}{dx}:

16x=5y4dydx16x = 5y^4 \cdot \frac{dy}{dx}

dydx=16x5y4\frac{dy}{dx} = \frac{16x}{5y^4}

Thus, y=16x5y4y' = \frac{16x}{5y^4}.

(b) Solve the equation explicitly for yy and differentiate to get yy' in terms of xx.

First, solve for y5y^5 in terms of xx:

y5=8x29y^5 = 8x^2 - 9

Now solve for yy:

y=(8x29)1/5y = \left(8x^2 - 9\right)^{1/5}

Next, differentiate this explicitly to find yy'. Using the chain rule:

y=ddx((8x29)1/5)y' = \frac{d}{dx} \left( \left(8x^2 - 9\right)^{1/5} \right)

Applying the chain rule:

y=15(8x29)4/5ddx(8x29)y' = \frac{1}{5} \left(8x^2 - 9\right)^{-4/5} \cdot \frac{d}{dx} (8x^2 - 9)

The derivative of 8x298x^2 - 9 with respect to xx is 16x16x, so:

y=15(8x29)4/516xy' = \frac{1}{5} \left(8x^2 - 9\right)^{-4/5} \cdot 16x

Thus:

y=16x5(8x29)4/5y' = \frac{16x}{5 \left(8x^2 - 9\right)^{4/5}}

(c) Check that your solutions to parts (a) and (b) are consistent by substituting the expression for yy into your solution for part (a).

From part (a), we had:

y=16x5y4y' = \frac{16x}{5y^4}

Substitute y=(8x29)1/5y = \left(8x^2 - 9\right)^{1/5} into this equation. Since y4=(8x29)4/5y^4 = \left(8x^2 - 9\right)^{4/5}, we get:

y=16x5(8x29)4/5y' = \frac{16x}{5 \left(8x^2 - 9\right)^{4/5}}

This matches the result from part (b), confirming that both answers are consistent.


Would you like further details or have any questions?

Here are 5 related questions to consider:

  1. What is implicit differentiation, and how does it differ from explicit differentiation?
  2. How can you apply the chain rule to differentiate composite functions?
  3. Why is it important to check consistency between implicit and explicit differentiation?
  4. How can you solve for higher-order derivatives in implicit differentiation problems?
  5. How would you approach similar problems where the powers of xx and yy are more complex?

Tip: Always ensure that you properly apply the chain rule when differentiating implicitly, especially when dealing with higher powers of functions.

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Math Problem Analysis

Mathematical Concepts

Implicit Differentiation
Explicit Differentiation
Algebra
Derivatives

Formulas

Implicit differentiation: d/dx [8x^2 - y^5] = d/dx [9]
Explicit differentiation of y = (8x^2 - 9)^(1/5)

Theorems

Chain Rule
Power Rule

Suitable Grade Level

College-level Calculus