Have no idea.. please help

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Lovely918

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Jun 25, 2012
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Okay I can't find an example problem on this so what do you think about this problem? My questions are in bold.

III. Consider the differential equation
where I''+I=e^it where i= sqrt (-1)
So would you just plug in i? into the equation?


a) Find c such that I(t)=cte^it is a solution.

Is the equation given what the problem is differentiated? then would you just solve for c?




b) Find the general solution and discuss what happens as t approaches infinity .

How would you incorporate an infinity?
 
KristinaR10 said:
Okay I can't find an example problem on this so what do you think about this problem? My questions are in bold.

III. Consider the differential equation
where I''+I=e^it where i= sqrt (-1)
So would you just plug in i? into the equation?

This question does not make sense


a) Find c such that I(t)=cte^it is a solution.

Is the equation given what the problem is differentiated? then would you just solve for c?

Weird way to put it - but yes



b) Find the general solution and discuss what happens as t approaches infinity .

How would you incorporate an infinity?

By taking limit to infinity!
Click to expand...

Are you taking an on-line course?
 
KristinaR10 said:
III. Consider the differential equation
where I''+I=e^it where i= sqrt (-1)

So would you just plug in i? into the equation?
Click to expand...

We cannot "just plug in i" because i never comes with any power cord. :razz:

Seriously, though, if you are asking whether to substitute the value i for the independent variable (t) in the given differential equation, then the answer is no.

I" + I = e^(i*t) is nothing more than part of this exercise's problem statement. In this exercise, you do not need to evaluate the expression e^(i*t) for any value of t.

In other words, part III requires no response because it's not asking a question.

The questions are parts (a) and (b).

Our question: Do you know how to calculate the second derivative of this?

c*t*e^(i*t)



PS: Note that I texted grouping symbols around the exponent. The grouping symbols are very important; do not omit them.

Without the grouping symbols, your expression e^it denotes:

\(\displaystyle e^{i} \cdot t\)
 
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The second derivative of
c*t*e^(i*t) is
-c e^(i t) (-2 i+t)

Is that part of a or b. Im sorry im so lost I just don't know what everything is asking.


mmm4444bot said:
We cannot "just plug in i" because i never comes with any power cord. :razz:

Seriously, though, if you are asking whether to substitute the value i for the independent variable (t) in the given differential equation, then the answer is no.

I" + I = e^(i*t) is nothing more than part of this exercise's problem statement. In this exercise, you do not need to evaluate the expression e^(i*t) for any value of t.

In other words, part III requires no response because it's not asking a question.

The questions are parts (a) and (b).

Our question: Do you know how to calculate the second derivative of this?

c*t*e^(i*t)



PS: Note that I texted grouping symbols around the exponent. The grouping symbols are very important; do not omit them.

Without the grouping symbols, your expression e^it denotes:

\(\displaystyle e^{i} \cdot t\)
Click to expand...
 
If you were given the polynomial equation \(\displaystyle x^5- 3x^4+ 2x^3- x^2+ x+ 4= 0\) and asked to show that x=2 was a solution what would you do?

You are given that \(\displaystyle I(t)= Cte^{it}\) and you have correctly calculated that \(\displaystyle I''= Ce^{it}(t- 2i)\). Now what is I''+ I?
 
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