Math Problem Statement

y' + 20y = 24, is y(x) = 6/5 - e^-2x a solution?

Solution

To determine whether y(x)=65e2xy(x) = \frac{6}{5} - e^{-2x} is a solution to the differential equation y+20y=24y' + 20y = 24, we need to:

  1. Calculate the derivative of y(x)y(x), i.e., y(x)y'(x).
  2. Substitute y(x)y(x) and y(x)y'(x) into the given equation y+20y=24y' + 20y = 24 and check if it holds true.

Step 1: Find y(x)y'(x)

Given that: y(x)=65e2xy(x) = \frac{6}{5} - e^{-2x} Let's differentiate it with respect to xx: y(x)=ddx(65e2x)y'(x) = \frac{d}{dx} \left( \frac{6}{5} - e^{-2x} \right) The derivative of 65\frac{6}{5} is 0 because it's a constant, and the derivative of e2x-e^{-2x} is 2e2x2e^{-2x} (using the chain rule): y(x)=2e2xy'(x) = 2e^{-2x}

Step 2: Substitute into the equation

Now we substitute y(x)=65e2xy(x) = \frac{6}{5} - e^{-2x} and y(x)=2e2xy'(x) = 2e^{-2x} into the differential equation y+20y=24y' + 20y = 24.

y+20y=2e2x+20(65e2x)y' + 20y = 2e^{-2x} + 20\left( \frac{6}{5} - e^{-2x} \right) Simplify the expression: =2e2x+20×6520e2x= 2e^{-2x} + 20 \times \frac{6}{5} - 20e^{-2x} =2e2x+2420e2x= 2e^{-2x} + 24 - 20e^{-2x} =(2e2x20e2x)+24= (2e^{-2x} - 20e^{-2x}) + 24 =18e2x+24= -18e^{-2x} + 24

Step 3: Check if the equation holds

For the equation to hold true, we need the expression 18e2x+24-18e^{-2x} + 24 to equal 24: 18e2x+24=24-18e^{-2x} + 24 = 24 Subtract 24 from both sides: 18e2x=0-18e^{-2x} = 0 This implies that: e2x=0e^{-2x} = 0 However, e2xe^{-2x} is never 0 for any real xx, so this leads to a contradiction.

Conclusion:

Thus, y(x)=65e2xy(x) = \frac{6}{5} - e^{-2x} is not a solution to the differential equation y+20y=24y' + 20y = 24.


Would you like more details on why this happens or a breakdown of any steps?

Here are some related questions to explore:

  1. How would you solve a first-order linear differential equation like y+20y=24y' + 20y = 24?
  2. What are the general methods to check if a given function is a solution to a differential equation?
  3. Can we find an explicit solution to y+20y=24y' + 20y = 24 using an integrating factor?
  4. How do you handle the case where eax=0e^{ax} = 0 in differential equations?
  5. What are some common types of solutions for linear differential equations?

Tip: When checking if a function is a solution, always differentiate it first and then plug both the function and its derivative back into the original equation to verify.

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Math Problem Analysis

Mathematical Concepts

Differential Equations
First-Order Linear Differential Equations
Derivatives
Substitution Method

Formulas

y' + 20y = 24
y'(x) = 2e^-2x
Substitution into differential equation

Theorems

Chain Rule
Checking Solutions to Differential Equations

Suitable Grade Level

Grades 11-12