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math problem, I lost my marbles it seems

jasin333

May 1, 2017
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B = R2 / R1 + R2

Simple voltage divider formula. B is the ratio. Now how can I solve for R2 if B = 0.462 and R1 = 1000?

I have gotten as far as R = 0.462/1 * R +1000/1 and I am stuck. I know I have to continue simplifying the equation, but it doesn't make sense. This is not actual homework, but I asked it here so I could be coaxed to remember the correct procedure.
 

Alec_t

Jul 7, 2015
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Re-arrange the formula :-
B =R2*(1/R1 + 1)
mod edit: deleted full solution. From here on it'S up to the op to show us he understands and can contine on his own feet.
 
Last edited by a moderator:

Harald Kapp

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@Alec_t : In the homework section it is our policy not to provide complete solutions, please. Rather we try to guide the op to finding the solution himself. This will help him solve similar problems in the futurre without resorting to other people.

Thanks for considering this in the future.
 

jasin333

May 1, 2017
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wait, what? stop editing post before I can read them. Or at least edit it to have some clarity. I know this is the homework section, but as long as someone is explaining the procedure, I COULD CARELESS about the answer. I want to understand the process, that could very well include the answer for all I care.

So don't just edit post unless you are going to add some value!!!
 

Harald Kapp

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So don't just edit post unless you are going to add some value!!!
I did ;),
What I forgot was to undelete the thread after editing it. I beg your pardon for that oversight. It is corrected now.

The additional value of my edit lies in you being able to find the solution yourself rather than being fed an instant meal.
 

jasin333

May 1, 2017
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ok, I finally got the correct answer. Thanks for the tip

Isolate R2 by multiplying both sides by the reciprocal of 1/R1+1
That left me with (R1+1)*B = R2. This seems to work, am I good?
 

duke37

Jan 9, 2011
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Your original equation is wrong.
You print B= R2/R1 + R2
It should be
B= R2/(R1 + R2)
 

Arouse1973

Adam
Dec 18, 2013
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Ok lets start by removing those brackets and the division sign... Do you know where to start?
Adam
 

Harald Kapp

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B= R2/(R1 + R2)
start by multiplying both sides of the equation by (R1+R2), then resolve the brackets, bring all terms containing R2 on one side only of the equation. Then isolate R2 and you're done.
It takes 5 steps (including the first multiplication).
 

Arouse1973

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That's the first one done with a good clue from Harald.
Thanks
Adam
 

duke37

Jan 9, 2011
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Remember
You can multiply both sides of an equation with the same factor.
You can add or subtract the same amount from each side of the equation.
You cannot get the right answer if you start with the wrong equation you have to be very picky.
 

Laplace

Apr 4, 2010
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If it is difficult to remember the rules for algebraic manipulation & solution, one alternative is to use symbolic algebra software. There are many products available, some even free for use online, such as the example attached.
Maxima-online.png
 

Harald Kapp

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one alternative is to use symbolic algebra software
In my opinion this is an alternative only once you know the basics. The software can relieve you from the boring work. But without having a fundamental understanding of the underlying principles you risk trusting in results that may actually be wrong (e.g. due to having neglected any boundary conditions, limits etc.)

In this case I strongly encourage @jasin333 to find the solution without the help of software.
 

jasin333

May 1, 2017
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Ok, so I do have the solution, but I am still struggling with the concepts. Trying to remember if I even did this sort of math... Maybe this is past where I went to, anyway, this is where I got to before I had to dive in for more help

for simplicity sake

B=X/(Y+X)
Step 1. Multiple both sides by (Y+X), because variables in denominators...
X=B(Y+X)
Step 2. Expand
X=BX + BY
Step 3. this is where I got stuck, my instinct told me to divide by X, but that makes no sense
I am now aware that I need to get the X's back together, so I should subtract BX
BY=X-BX
Step 4. I still don't get this step, explanation needed please
 

duke37

Jan 9, 2011
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You are doing well:)

It is normal to put a full stop between letters to act as a multiplication sign. i.e. BX is written as B.X

Step 4
B.Y=X-B.X
take out X so
B.Y=X(1-B)
Step 5
Divide both sides by (1-B) to get X

Q.E.D
At school we didn't do latin so the maths teacher said it was 'quite easy done';)
 
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