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#### timmay7

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i want to go to bed, and im really tired, and i cant remember what to do. I have s as one denominator and s-1 as another. What do i need to multiply these two with to get my common denominator? A friend told me s(s-1) but i cant seem to get it to work :S<br><br>
probably sounds rediculous but i ALWAYS forget these small things when im tired, and its due tomorrow..

#### rabidgnome229

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<div>Originally Posted by <strong>timmay7</strong></div>
<div style="font-style:italic;">i want to go to bed, and im really tired, and i cant remember what to do. I have s as one denominator and s-1 as another. What do i need to multiply these two with to get my common denominator? A friend told me s(s-1) but i cant seem to get it to work :S<br><br>
probably sounds rediculous but i ALWAYS forget these small things when im tired, and its due tomorrow..</div>
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if your equation has the form A = B/s + C/(s-1) then you do want to multiply the entire thing by s(s-1) to get A*s(s-1) = B(s-1) + Cs<br>
solve from there<br><br>
or if you just have the expression<br>
B/s + C/(s-1) multiple B/s by (s-1)/(s-1) and C/(s-1) by s/s to get B(s-1)/(s(s-1)) + CS/(s(s-1))

#### timmay7

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i just skipped it. The question is (1/s-1/s-1)/(1/s)

#### d3daiM

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yeah, <br />
<br />
you say you have (1/s-1/s-1)/(1/s)?<br />
<br />
so that's be (1/s)/(1/s)-(1/s)/(1/s)-1/(1/s)=<br />
<br />
0-1/(1/s)=<br />
<br />
-1/(1/s).

#### sccr64472

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<div style="margin:20px; margin-top:5px; ">
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Originally Posted by <strong>timmay7</strong>

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<div style="font-style:italic">i just skipped it. The question is (1/s-1/s-1)/(1/s)</div>

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</div>What did they ask you to do? Simplify the expression? If so, it's extremely easy if you look closely at it....<br />
<br />
(1/s - 1/s -1)/(1/s) = (0 - 1)/(1/s) since the first 2 expression can be combined and add to 0.<br />
<br />
This leaves you with........ -1/(1/s)...flipping the denominator and multiplying..<br />
<br />
-1(s) = -s

#### rabidgnome229

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Originally Posted by <strong>timmay7</strong>

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<div style="font-style:italic">i just skipped it. The question is (1/s-1/s-1)/(1/s)</div>

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</div>equals what?<br />
<br />
**EDIT**<br />
@people above<br />
it is not 1/s - 1/s - 1<br />
it is 1/s - 1/(s-1)

#### d3daiM

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Originally Posted by <strong>D3DAiM</strong>

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<div style="font-style:italic">yeah, <br />
<br />
you say you have (1/s-1/s-1)/(1/s)?<br />
<br />
so that's be (1/s)/(1/s)-(1/s)/(1/s)-1/(1/s)=<br />
<br />
0-1/(1/s)=<br />
<br />
-1/(1/s).</div>

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</div>= -s^-1

#### rottenotto

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So, it's (1/s-1/(s-1))/(1/s)?

#### timmay7

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<div style="margin:20px; margin-top:5px; ">
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Originally Posted by <strong>rabidgnome229</strong>

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<div style="font-style:italic">equals what?<br />
<br />
**EDIT**<br />
@people above<br />
it is not 1/s - 1/s - 1<br />
it is 1/s - 1/(s-1)</div>

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</div>yeah thanks for the correcion, should have mentioned it. The answer should be 1/1-s. Have fun while i snore in bed and ill finish the simplification tomorrow, if you can help me multiply in s(s-1) whit the rest. Thx <img src="/images/smilies/biggrin.gif" border="0" alt="" title="Big Grin" class="inlineimg" />

#### d3daiM

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<div style="margin:20px; margin-top:5px; ">
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Originally Posted by <strong>rabidgnome229</strong>

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<div style="font-style:italic">equals what?<br />
<br />
**EDIT**<br />
@people above<br />
it is not 1/s - 1/s - 1<br />
it is 1/s - 1/(s-1)</div>

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</div>Ohhh<br />
<br />
ok then, do the "diagonal-diagonal-across" method to get a common denominator..<br />
<br />
([(s-1)(1/s)]-1)/(s-1)

#### rabidgnome229

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the simplification you posted equals -s - not -1/s<br />
<br />
if you just have to simplify<br />
<br />
(1/s - 1/(s-1))/(1/s) = s(1/s - 1/(s-1)) = s/s - s/(s-1) = 1 - s/(s-1) = (s-1)/(s-1) - s/(s-1) = (s-1-s)/(s-1) = <b>-1/(s-1)</b> = 1/-(s-1) = <b>1/(1-s)</b>

#### sccr64472

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<div style="margin:20px; margin-top:5px; ">
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Originally Posted by <strong>D3DAiM</strong>

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<div style="font-style:italic">= -s^-1</div>

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</div>Nope, try it again.

#### d3daiM

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<div style="margin:20px; margin-top:5px; ">
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<div style="font-style:italic">Nope, try it again.</div>

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</div>For the other equation..

#### sccr64472

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<div style="margin:20px; margin-top:5px; ">
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<div style="font-style:italic">For the other equation..</div>

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</div>I know, it's the incorrect answer for both.

#### timmay7

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<div style="margin:20px; margin-top:5px; ">
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Originally Posted by <strong>rabidgnome229</strong>

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<div style="font-style:italic">the simplification you posted equals -s - not -1/s<br />
<br />
if you just have to simplify<br />
<br />
(1/s - 1/(s-1))/(1/s) = s(1/s - 1/(s-1)) = s/s - s/(s-1) = 1 - s/(s-1) = (s-1)/(s-1) - s/(s-1) = (s-1-s)/(s-1) = <b>-1/(s-1)</b> = 1/-(s-1) = <b>1/(1-s)</b></div>

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</div>correct answer but i dont quite follow you <img src="/images/smilies/tongue.gif" border="0" alt="" title="Stick Out Tongue" class="inlineimg" />

#### rabidgnome229

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(1/s - 1/(s-1))/(1/s) = s/1 * (1/s - 1/(s-1))<br>
s(1/s - 1/(s-1)) = s/s - s/(s-1) = 1 - s/(s-1)<br><br>
to add these multiply the 1 by (s-1)/(s-1) to get<br>
(s-1)/(s-1) - s/(s-1) = ((s-1) - s)/(s-1) = (s-1-s)/(s-1)=-1/(s-1)<br><br>
since: -a/b = a/-b<br>
-1/(s-1) = 1/(-1(s-1))<br><br>
since: -1(s-1) = -s + 1 = 1-s<br>
1/(-1(s-1)) = 1/(1-s)<br><br>
If you're still confused where did I lose you?

#### timmay7

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nvm my dad explained it to me. you want the common denominator s(s-1) so you multiply it up to get that, then you wipe the denominators, simplify, then multiply both sides with -1 and you end up with 1/(1-s). thx all anyways <img alt="" class="inlineimg" src="/images/smilies/smile.gif" style="border:0px solid;" title="Smile">

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