Newbie question on equations

Thread Starter

OBIE

Joined Feb 28, 2012
11
Hello,
I've been going thru the worksheets and came across some algebra manipulations that were beyond me.
The question is:
Manipulate this equation to solve for resistor value R1, given the values of R2 and Rparallel:

Rparallel = R1 R2
R1 + R2The answer is

R1 = R2 Rparallel/ R2 − Rparallel


Appologies for the bad paste job
The question is
How do you get from the first equation to solve for R1?
 

MrChips

Joined Oct 2, 2009
30,618
The answer you are looking for is

\(\frac{1}{R} = \frac{1}{R1} + \frac{1}{R2}\)

Hence to solve for R1

\(\frac{1}{R1} = \frac{1}{R} - \frac{1}{R2} \)

\(\frac{1}{R1} = \frac{R2 - R}{R . R2}\)

\(R1 = \frac{R . R2}{R2 - R}\)
 

Thread Starter

OBIE

Joined Feb 28, 2012
11
Hello Mr. Chips
Thank you for your reply.
I am familiar with summing the reciprocals for a parallel circuit and can solve those without any problem.
The equation I am dealing with is an alternate, and it said that it is only used for 2 resistors in parallel.

Rparallel= R1xR2/R1+R2
The question is: solve for R1
The answer given is
R1=R2xRparallel/R2-Rparallel
The answer is plain algebraic manipulation, but this one escapes me and I'd appreciate a step by step procedure
Thank you
Obie (John)
 

Thread Starter

OBIE

Joined Feb 28, 2012
11
Hello Crutshow,
Beautiful!
Now that I see it, it's so simple. I hope with a bit more practice that I'll be able to handle most equations.
Many thanks,
Obie
 
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