MAT1085 assignment

[t3nsai]

Am I allowed to ask for help on the assignment :T?

[m@tty]

Go ahead.

EDIT:
Is it by any chance 2.f) ? I had trouble with that.

[t3nsai]

firstly, i need to point out  i don't understand what i am doing so yeah XD

y" + 9y' + 20y = 72e^(-4x)   , sorry I don't know how to use that latex program

well this is what I did:

rē+9r+20=0
r= -4 r=-5
so y(c)= C1e^(-4x) + C2e^(-5x)


then Y(p) = Ae^(-4x)  therefore Y'(p) = -4Ae^(-4x) and so on..
subbed it  into the particular equation ( i think that's what it is called)

so I get the equation 16A-36A+20A=72  <- this is where i'm stuck   0=72 :S

[enwiabe]

tensai, whenever this happens you should try multiplying your trial function by 'x' or perhaps even 'x^2'

so now try:
Y(p) = Axe^x

and if that fails

try

Y(p) = Ax^2e^x

a particular solution of an ODE is often inspired guesswork so good luck and let me know if htis works

[m@tty]

firstly, i need to point out  i don't understand what i am doing so yeah XD

y" + 9y' + 20y = 72e^(-4x)   , sorry I don't know how to use that latex program

well this is what I did:

rē+9r+20=0
r= -4 r=-5
so y(c)= C1e^(-4x) + C2e^(-5x)


then Y(p) = Ae^(-4x)  therefore Y'(p) = -4Ae^(-4x) and so on..
subbed it  into the particular equation ( i think that's what it is called)

so I get the equation 16A-36A+20A=72  <- this is where i'm stuck   0=72 :S

Wait, which assignment is this? I can't see anything like that in assignment 3...

[t3nsai]

assessment assignment!


thank you for helping
 I'll try your method enwiabe


edit: assessment assignment 2 question 4

[t3nsai]

tensai, whenever this happens you should try multiplying your trial function by 'x' or perhaps even 'x^2'

so now try:
Y(p) = Axe^x

and if that fails

try

Y(p) = Ax^2e^x

a particular solution of an ODE is often inspired guesswork so good luck and let me know if htis works

thanks :DD it does work!  I got A= 72

[t3nsai]

Okay another question:

How exactly do I use the Macluarin series to find an exact value?

given (some symbol notation infinity n=1 thing here)  3^n/n!

you guys don't have to solve it for me but any hints/advice would definitely help

[TrueTears]

just sub in the values needed...?

[t3nsai]

I don't understand >_<

Isn't there diffing involved :S?

[TrueTears]

Yea, to get the Macluarin series you would need to differentiate, then you'd just sub the respective values in. Do you have a specific example?

[kamil9876]

seems like a matter of just noticing that it is the series for (-1 because we are starting from n=1 so the n=0) term is missing. And so sub in x=3.

[t3nsai]

well the question was use the maclaurin series to determine the exact value of 3^n/(n!)


when do I stop after how many terms?

lol i think my main issue was differentiating 3^n
 
  

[Gloamglozer]

I'm doing this right now in Calculus 2 at UoM...  It's part of enhancement studies at Monash?

[t3nsai]

yep,


finally finished my assignment today so relieved now i can concentrate on my vce subjects x_x