How Can You Eliminate Constants in a Differential Equation?

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In summary, to eliminate the constants c1 and c2 and create a differential equation from y, y', and y'', one can plug y = (c1 +c2x)ex for the second term in y' and solve for c2, resulting in the differential equation c2 = (y' - y) e^-x.
  • #1
th3chemist
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Homework Statement



eliminating c1 and c2 from y, y' and y'' to create a differential equation

Homework Equations



I have the equation y = (c1 +c2x)e^x
y' = c2e^x +(c1+c2x)e^x
y'' = c2e^x + c2e^x + (c1+c2x)e^x)

(from product rule)

The Attempt at a Solution



I'm just not sure how to eliminate the constants. If I try to do y'' - y i still have constants left.
 
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  • #2
th3chemist said:

Homework Statement



eliminating c1 and c2 from y, y' and y'' to create a differential equation

Homework Equations



I have the equation y = (c1 +c2x)e^x
y' = c2e^x +(c1+c2x)e^x
y'' = c2e^x + c2e^x + (c1+c2x)e^x)

(from product rule)

The Attempt at a Solution



I'm just not sure how to eliminate the constants. If I try to do y'' - y i still have constants left.
What do you get if you plug y = (c1 +c2x)ex for the second term in y' ?

Solve that for c2.
 
  • #3
with y"-y you are only using part of you available information.
What happens if you subtract y-y' = ... ?
or y'-y" ?
 
  • #4
SammyS said:
What do you get if you plug y = (c1 +c2x)ex for the second term in y' ?

Solve that for c2.

thank you! I can't believe I didn't see that.

I got c2 = (y' - y)/ e^x. I can then sub this into y'' to get the differential.

Thank you :)
 
Last edited:
  • #5
th3chemist said:
thank you! I can't believe I didn't see that.

I got c2 = (y' - y) e^x. I can then sub this into y'' to get the differential.

Thank you :)

Isn't it c2 = (y' - y) e^-x ?
 
  • #6
lendav_rott said:
Isn't it c2 = (y' - y) e^-x ?

yes yes, for some reason it didn't put the / button
 

1. What is the purpose of eliminating constants in scientific research?

Eliminating constants helps to isolate and identify the effects of independent variables in an experiment. It allows for more accurate and reliable conclusions to be drawn.

2. How do you determine which constants to eliminate?

Constants that are not relevant to the research question or hypothesis can be eliminated. It is important to carefully consider which variables are truly independent and which may be influenced by other factors.

3. Can eliminating constants lead to biased results?

No, eliminating constants does not in itself lead to biased results. However, it is important to carefully consider which constants are eliminated and to ensure that the remaining variables are truly independent.

4. Are there any situations where eliminating constants is not necessary?

In some experiments, constants may not need to be eliminated if they do not have a significant impact on the independent variable. However, it is always important to carefully consider the potential effects of all variables in an experiment.

5. What are some potential challenges in eliminating constants?

Identifying which variables are truly independent and which may be influenced by other factors can be challenging. Additionally, eliminating constants may limit the generalizability of the results, as the experiment may not accurately reflect real-world conditions.

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