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#1 Help Me ! » Help with Laplace transform please » Yesterday 16:47:11

mrpace
Replies: 0

determine the laplace transform of f(t) of the following


f(t) =         
        e^(-t)   when 0 ≤ t ≤ 5
        -1  when t > 5

I got my answer as simply 1/(s+1) when 0 ≤ s ≤ 5
                                    -1/s when s > 5

I'm not sure if this is right though.

#2 Help Me ! » Linear Transformation problem » 2014-09-11 14:06:37

mrpace
Replies: 1

Find all real values of a and b such that the following is a reflection

T:  X  =  aX + (24/25)Y
     Y      bY + (24/25)X     

Sorry for the lack of latex; I'm sure you can work it out.

#3 Re: Help Me ! » Prove this limit » 2014-09-11 03:01:03

Agnishom wrote:

There is no need to factor it. You are confusing yourself by factoring it

Really? I'm trying with it not factored and not having any luck.. can you help?

#4 Help Me ! » Prove this limit » 2014-09-11 02:01:47

mrpace
Replies: 3

show, using the formal definition of a limit, that:

lim
             x^2=4
x -> 2 

I'm getting to a point where I have |x+2||x-2| < E

But I don't know where to go from there. Help is much appreciated.

#5 Help Me ! » Help with plane rotations?? » 2014-09-10 16:11:36

mrpace
Replies: 1

Find a sequence of plane rotations that transform x = [6  6  17] to a multiple of [1  0  0].

Any ideas??

#6 Help Me ! » Linear algebra help?? » 2014-09-09 14:02:29

mrpace
Replies: 3

Show that if A and B represent reflections in R3, then AB represents a rotation in R3.

Any help is appreciated.

#7 Help Me ! » Check my answer please » 2014-08-16 16:35:19

mrpace
Replies: 1

A force of 400 N stretches a spring 2 meters. A mass of 50 kg is attached to the
end of the spring and is initially released from the equilibrium position with an
upward velocity of 10 m/s. Find the equation of motion

My answer is x=5sin(2t)

If youu get something different, can you show me how you got it please?
Cheers.

#8 Help Me ! » General solution for this differential equation?? » 2014-08-16 12:48:30

mrpace
Replies: 2

Find a general solution to

y′′′ − y′′ + 2y = 0

I have never dealt with 3rd order D.E before. I hope you have!

#9 Help Me ! » Help with differential equation problem please » 2014-08-16 12:44:52

mrpace
Replies: 1

Given that y1 = x^(-2) , find a second linearly independent solution to

(x^2)y′′ + 6xy′ + 6y = 0, x > 0.

Any help would be much appreciated.

#10 Re: Help Me ! » Challenging proof. » 2014-08-14 00:04:27

Hey that's really nice. Just one thing. How would you say in English min{d1,d2,d}?

and i see where the d1 and d2 come from in the brakets above, but where does the d come from??

d=delta obv.

#11 Help Me ! » Challenging proof. » 2014-08-13 21:49:20

mrpace
Replies: 3

Prove that if lim   f(x) =   lim   g(x) = b, and if there exists a number δ > 0 such that...
                 x→a           x→a       

0 < |x − a| < δ ⇒ f(x) ≤ h(x) ≤ g(x)

then   lim  h(x) = b.
        x→a 


Worked on this for a while without getting anywhere. Any ideas???

#12 Help Me ! » please help. » 2014-08-12 02:33:37

mrpace
Replies: 8

If f(x) = ax + b for all real numbers x, where a and b are numbers, find for what values
of a and b is it true that ff = f o f?

Not sure what it means by ff or f o f. Help is much appreciated.

#13 Re: Help Me ! » Help with this weird question?? » 2014-08-11 22:32:24

bob bundy wrote:

hi mrpace

Because the definition comes in two parts, the answer will too.

x ≥ 0 :

x < 0

You could argue that f(0) is undefined when x < 1 and therefore this second answer cannot be determined but I don't think that is intended.

I have used Latex.  If you click on the expression above you'll get a window that shows the code for this.  You have to add at the start square brackets math, and complete the code with square brackets /math

Thus:

  [math]\frac{h^2 - 0}{h} = \frac{h^2}{h} = h[/math]

There's a tutorial to get you started here:

http://www.mathisfunforum.com/viewtopic.php?id=4397

The first few posts in that thread will be enough to get you started.  There's an editor at:

http://latex.codecogs.com/eqneditor/editor.php

Bob


Great. I see how it works now. Thanks a lot.

#14 Help Me ! » Help with this weird question?? » 2014-08-11 16:48:25

mrpace
Replies: 2

If f(x) = x^2  if x is greater than or equal to zero.
         = 1 if x is less than zero

then find an expression for the following:

[f(h) - f(0)] / h

h can't equal zero obviously

I don't know how to do these problems so any help is appreciated.

Sorry for the lack of latex...i tried to learn but i don't get it.

#15 Help Me ! » Magnitude of complex vector? » 2014-08-05 19:00:10

mrpace
Replies: 1

u = [i, 2i]

v = [2-i, 1+i]

find |u| and |v|

Not sure on this.

#16 Help Me ! » Linear algebra proof » 2014-08-05 17:24:26

mrpace
Replies: 1

Let T : V --> W be a linear transformation with ker(T) = {0}

Suppose u1, u2 ∈ V are linearly independent.

Prove that T(u1) and T(u2) are linearly independent vectors in W.



Just not sure how to construct this. Any help would be great, thanks.

#17 Re: Help Me ! » Solve the initial value problem » 2014-07-30 20:22:07

bobbym wrote:

Use codecogs, I sent you the link already.

cool, thanks. Are you able to help me with this question?

#18 Help Me ! » Solve this differential equation » 2014-07-30 19:45:13

mrpace
Replies: 2

dy + y³x+y=0
dx

solve

Looks innocent but I can't figure.

Sorry for all the DE questions, I have a russian lecturer who I can't understand so I need to learn somewhere sad

#19 Re: Help Me ! » Solve the initial value problem » 2014-07-30 19:23:39

bobbym wrote:

Hi;

Is this what you want?

or



with y(1)=1?

the 2nd one sorry. I don't know how you do those nice symbols haha.

#20 Re: Help Me ! » Solve the differential equation » 2014-07-30 19:09:06

bobbym wrote:

Integrate both sides which will eliminate the differentials dx and dy.

Thanks a lot. Would you be able to help me with my initial value problem that i just posted?

#21 Help Me ! » Solve the initial value problem » 2014-07-30 18:58:21

mrpace
Replies: 5

dy  +  3y  +  2  =  3x   ,  y(1)=1
dx       x


Not sure how to go about this one.

#22 Help Me ! » Challenging integral » 2014-07-30 17:23:36

mrpace
Replies: 1

Integrate    dx             or     1     *dx
              xcos(v)            xcos(v) 

any idea?

#23 Re: Help Me ! » Solve the differential equation » 2014-07-30 17:01:03

bobbym wrote:

The DE is separable:

Now can you integrate both sides?


Ok so what does it mean by solving explicitly for the y differential equation? do i only intergrate the side with the y or what?

#24 Help Me ! » Solve the differential equation » 2014-07-30 15:43:46

mrpace
Replies: 5

Solve explicitly for the y differential equation.

dy  =  3x^2(1+y^2)
dx

I don't really know what this means. Any help means a lot.

#25 Help Me ! » Does this sequence converge or diverge? » 2014-07-29 17:09:31

mrpace
Replies: 6

n+1
(-1 )^(n-1) * 2n+1

what happens as n goes to infinity?

My thoughts are that it oscillates between near 0.5 and -0.5 but never hits either. does this mean it diverges?

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