partial fraction/ laplace

2010-12-06 8:21 pm
請問這個點做呢.....::
partial fraction請比D意見..
應該點拆係最好/最快?
拆完之後可以點計出ABCD?
THX^^



圖片參考:http://img89.imageshack.us/img89/3446/tulaplace.png
更新1:

L^-1......??

回答 (1)

2010-12-06 11:11 pm
✔ 最佳答案
Let A/s^3+B/s^2+C/s+D/(s-4)=(s-2)/[s^3(s-4)]

Multiply both sides by s^3 and let s->0 =>A=1/2
Multiply both sides by s-4 and let s->4 =>D=1/32

Now 1/[2s^3]+B/s^2+C/s+1/[32(s-4)]=(s-2)/[s^3(s-4)]

Multiply both sides by s and let s->infinity
=>0+0+C+1/32=0
=>C=-1/32

Finally, sub. s=1 into the new equation, we have
1/2+B-1/32-1/96=1/3
B=-1/8

So, 1/[2s^3]-1/[8s^2]-1/[32s]+1/[32(s-4)]=(s-2)/[s^3(s-4)]

You can check the answer by sub. some other values of s.


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