Brushing up on the basics of diff eq

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Homework Help Overview

The discussion revolves around solving a differential equation of the form y(x) = C1sin(2x) + C2cos(2x) with specific initial conditions. Participants are trying to understand how to derive the relationship between constants C1 and C2 based on the given condition y(∏/8) = 0.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants are attempting to manipulate the equation derived from the initial condition to find a relationship between C1 and C2. There are questions about the validity of certain assumptions regarding the constants and their simplifications.

Discussion Status

Some participants have offered guidance on manipulating the initial condition equation, while others are exploring the implications of their assumptions about the constants. Multiple interpretations of the problem are being discussed, particularly regarding the relationships between C1 and C2.

Contextual Notes

There is a mention of an additional initial condition y'(∏/8) = √2, which may influence the determination of C1 and C2, but this has not been fully explored in the discussion.

cowmoo32
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Homework Statement


y(x) = C1sin(2x) + C2cos(2x)

Homework Equations


y(∏/8) = 0


The Attempt at a Solution


C1(1/2)(√2) + C2(1/2)(√2) + 1 = 0


The book jumps to the equation below and I'm having trouble figuring out how they got there.
C1 + C2 = -√2
 
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cowmoo32 said:

Homework Statement


y(x) = C1sin(2x) + C2cos(2x)

Homework Equations


y(∏/8) = 0


The Attempt at a Solution


C1(1/2)(√2) + C2(1/2)(√2) + 1 = 0


The book jumps to the equation below and I'm having trouble figuring out how they got there.
C1 + C2 = -√2
What is the dif. eq. you're trying to solve?

Multiply your "attempt at a solution" by √2 .
 
Determine C1 and C2 so that y(x) = C1sin(2x) + C2cos(2x) will satisfy the initial conditions y(∏/8) = 0 and y'(∏/8) = √2
 
Multiply your "attempt at a solution" in your original post by √2 .
 
I guess it's safe to assume that C1/2 = C1 and C2/2 = C2 considering they're both unknowns at this point?
 
cowmoo32 said:
I guess it's safe to assume that C1/2 = C1 and C2/2 = C2 considering they're both unknowns at this point?
That doesn't make sense, unless you are asking if you can replace C1/2 by C1 and C2/2 by C2 .

If [itex]C_1+C_2=-\sqrt{2}\,,[/itex] then you can replace [itex]C_2[/itex] with [itex]-C_1-\sqrt{2}[/itex]
 

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