Can someone tell me how to put these partial fractions in line?
A/s + B/S^2 + C/S-1 + D/S-2
so I get
1 + 2S = A( ? ) + B( ? ) + C( ? ) + D( ? )
I know 2 and 3 partial fractions by memory so dont know how to figure 4 out
You need to be more careful with your parentheses. Technically, you wrote 1+((2s)/(S-1))(S-2)(S^2), not, as I suspect you mean, (1+2s)/((S-1)(S-2)(S^2)).)
Ok. I like your initial guess as to how to break down the partial fractions. In order to continue, you need to get a common denominator (which is always going to be equal to the original common denominator, so that's easy to figure out). Just multiply every fraction top and bottom by what's "missing" in that fraction's denominator. Example:
$\displaystyle \dfrac{A}{s}=\dfrac{As(s-1)(s-2)}{s^{2}(s-1)(s-2)}.$
Can you continue from here?
still not really what you mean. Im a final year electrical engineering student and can easily memorise formulas and apply them to problems but dont know how their derived. This is the same as the partial fractions I have only done 2 or 3 partial fractions and have memorised the positions but not sure why their in those positions so thats why I cant do this 4 partial fraction problem. If ya know what I mean.
No, no. You're skipping steps, for one thing, and you're not doing what I ask you, for another. See here:
1. In order to solve your problem, you need to understand the procedure of partial fractions thoroughly.
2. It seems to me that your biggest stumbling block with partial fractions (at least right now) is adding up your guesses on the RHS.
3. The basic procedure there is getting common denominators.
4. Therefore, I want to show you how you get common denominators.
Therefore, I want you to focus on the addition problem in post # 8. Show me the next step. How do you get the common denominators?