# Don't know how to factor?

• March 4th 2013, 09:10 AM
simplyComplex
Don't know how to factor?
Hello,

I have the following equation:

v1/v2 = R2/R1+R2

How do we solve for R2?

I don't know how to isolate R2 on one side of the equation. All help is appreciated?

thanks
• March 4th 2013, 09:29 AM
Plato
Re: Don't know how to factor?
[QUOTE=simplyComplex;773431]I have the following equation:
v1/v2 = R2/R1+R2
How do we solve for R2?/QUOTE]

Is it $\frac{v_1}{v_2}=\frac{R_2}{R_1+R_2}~?$

Because you actually posted $\frac{v_1}{v_2}=\frac{R_2}{R_1}+R_2$

Which is it?
• March 4th 2013, 09:53 AM
HallsofIvy
Re: Don't know how to factor?
If it is $\frac{v_1}{v_2}= \frac{R_2}{R_1+ R_2}$, start by multiplying both sides by $v_2(R_1+ R_2)$ to get $v_1(R_1+ R_2)= v_1R_1+ v_1R_2= v_2R_2$.

If it is $\frac{v_1}{v_2}= \frac{R_2}{R_1}+ R_2$, start by writing $R_2$ as $\frac{R_1R_2}{R_2}$ so you have $\frac{v_1}{v_2}= \frac{R_2}{R_1}+ \frac{R_1R_2}{R_1}= \frac{R_2+ R_1R_2}{R_1}$ and now multiply by $R_1v_2$.
• March 4th 2013, 10:47 AM
simplyComplex
Re: Don't know how to factor?
Ooops I'm sorry.... Its:

v1/v2 = R2/(R1 + R2)

Quote:

start by multiplying both sides by v2(R1 + R2) to get....
stop, you are going too fast for me!!!! If I start off with this:

v1/v2 = R2/(R1 + R2)

so when you say cross multiply... do you mean like this:
(R1 + R2) (v1/v2) = (R2/(R1+R2)) (v2)
v1(R1 + R2) = R2v2
v1R1 + v1R2 = R2v2

So now, R2 is on both sides, what I really need is to isolate R2 on one side!!!!
So what is the next step?

thanks
• March 4th 2013, 11:14 AM
simplyComplex
Re: Don't know how to factor?
Okay I think I got it:

v1/v2 = R2/(R1 + R2)
(R1 + R2) (v1/v2) = (R2/(R1+R2)) (v2)
v1(R1 + R2) = R2v2
v1R1 + v1R2 = R2v2
v1R1 = R2v2 - v1R2
v1R1 = R2(v2 - v1)

v1R1/(v2-v1) = R2(v2 - v1)/ (v2 - v1)

R2 = v1R1/(v2-v1)

Thanks!