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# I need help with solving an equation.

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Hello my lovely community, I have this equation :

0 = I1/r - I2/r+d

By the way the 1 at I1 is an index. Same goes for I2.

I want to solve this equation for r but I am helpless :(

Could anyone help me and show it to me step by step ?

Sekai  Oct 19, 2017
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#1
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Is the equation

0   =  I^(1/r) - I^(2/r) +  d     ????

Or is it

0  =  I^1  / r  +  I^(2) / r  + d      ????

CPhill  Oct 19, 2017
edited by CPhill  Oct 19, 2017
#2
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The 1 at I1 and the 2 at I2 are just an index. In this exaple I1 is electricity number 1 and I2 is electricity number 2 :)!

Theoretical I could write : 0 = y/r - x/r+d

and now I want to solve for r :3

Sekai  Oct 19, 2017
#3
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Oh...OK....I understand now

We have that

0  =  I1 / r  + I2 / r  + d     subtract   d from both sides

-d  =   I1 / r  + I2 / r       note that the right side can be written as

-d =   [  I1 + I2 ]  / r      multiply both sides by r

-rd  =   I1 + I        divide both sides by -d

r =     [  I1 + I2 ]  /  -d

r  =   - [ I1 + I2 ] / d

CPhill  Oct 19, 2017
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Thank you !

(I also learned to make an index. I<-- haha.)

Sekai  Oct 19, 2017
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P.S.  ......if the "d"  is supposed to be a part of the second denominator, we have

0  =  I1 / r  + I2 /  (r  + d)      get a common denominator

0 =   [ I1 ( r + d)  +  Ir ]  /  [ r (r + d) ]      multiply boh sides by   [ r (r + d) ]

0 *  [ r (r + d) ]  =   [ I1 ( r + d)  +  Ir ]

0  =   [ I1 ( r + d)  +  I2 r ]    simplify

0  =  I1 r + I1d +   I2 r       subtract  I1d  from both sides

- I1d     =    I1 r  +   I2 r      factor the right side

- I1d   =   r  [ I1 + I2 ]         divide both sides by  [ I1 + I2

- I1d  /   [ I1 + I2 ]    =   r

CPhill  Oct 19, 2017
#8
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Yessssss I was wondering the whole day about the equation since I've seen it before and it was more like the second one.

I am sry for my mistake but thanks that you're so mindfully!

Sekai  Oct 20, 2017
#6
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One last thing, Sekai

The  "1"    and  "2"   are known as "subscripts"

"Indexes"  usually refer to exponents

CPhill  Oct 19, 2017
#7
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Well I am learning Math and Physik in german and my teacher alway say to Subscripts index so I was assuming it was the same in english haha :c

But thanks.

Learning by mistakes ! :D

Sekai  Oct 20, 2017

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