Solving Non-Constant Coefficient Equation: Need Help!

In summary, the conversation discusses using substitution x = e^t to transfer an equation into one with constant coefficients and solving it. The speaker provides guidance on how to complete the substitution and solve the equation using the chain rule.
  • #1
hola
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1. Use substitution x = e^t to transfer equation into one with constant coefficients and solve:
x^2 y'' -3xy' + 13y = 4 + 3x
My work:
Okay, we have
e^2t y'' - 3e^t y' + 13y = 4 + 3e^t.

Now I am absolutely stuck. No idea how to solve it. Help!
 
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  • #2
You didn't complete the substitution! Your y' and y" are still with respect to x, not t.

Use the chain rule: dy/dx= dy/dt dt/dx. Since x= et, t= ln x and
dt/dx= 1/x. That is, dy/dx= (1/x)(dy/dt).
d2y/dx2= d((1/x)(dy/dt)/dx= (-1/x2)dy/dt+ (1/x)d(dy/dt)/dx= ((-1/x2)dy/dt+(1/x)(1/x)d2y/dt2=.
Now, x2 y'' = d2y/dt2- dy/dt
and -3xy'= -3 dy/dt
so the differential equation is
d2y/dt2- 4dy/dt+ 13y= 4+ 3ett

That should be easy to solve!
 

1. What is a non-constant coefficient equation?

A non-constant coefficient equation is an algebraic equation where the coefficients (numbers multiplied by the variables) change depending on the value of the variable. This makes the equation more complex and challenging to solve compared to a constant coefficient equation.

2. How do you solve a non-constant coefficient equation?

To solve a non-constant coefficient equation, you can use various methods such as substitution, elimination, or the quadratic formula. The specific method will depend on the type of equation and its degree (highest power of the variable).

3. Can a non-constant coefficient equation have multiple solutions?

Yes, a non-constant coefficient equation can have multiple solutions, especially if it is a higher degree equation. These solutions can be real or complex numbers, depending on the nature of the equation.

4. What are some common mistakes to avoid when solving a non-constant coefficient equation?

Some common mistakes to avoid when solving a non-constant coefficient equation include forgetting to distribute the coefficients, making calculation errors, and missing solutions by only considering real numbers.

5. Are there any tips for solving non-constant coefficient equations?

Yes, some tips for solving non-constant coefficient equations include simplifying the equation as much as possible, using a systematic approach (such as substitution or elimination), and checking your solutions by plugging them back into the original equation.

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