Rearranging Equation

**embob** · February 15th 2010, 02:12 AM

Im very-much out of practice... Almost feel guilty posting in 'Pre-University'

I'm trying to rearrange this equation for a electronic regulator,

$ Vout = (1.25 * ((1+R2)/R1)) + Iadj*R2 $

So that R2 is on its own. Im not sure what todo to cancel R2 on the left hand side...

$ R1 * ((Vout - (Iadj * R2))/1.25) - 1 = R2 $

Not sure how to use the maths tags properly.

Any help much appreciated.

**Prove It** · February 15th 2010, 02:23 AM

Originally Posted by embob

Im very-much out of practice... Almost feel guilty posting in 'Pre-University'

I'm trying to rearrange this equation for a electronic regulator,

$ Vout = (1.25 * ((1+R2)/R1)) + Iadj*R2 $

So that R2 is on its own. Im not sure what todo to cancel R2 on the left hand side...

$ R1 * ((Vout - (Iadj * R2))/1.25) - 1 = R2 $

Not sure how to use the maths tags properly.

Any help much appreciated.

So you want to solve for $R_2$ ...

$V_{\textrm{out}} = \frac{1.25(1 + R_2)}{R_1} + I_{\textrm{adj}}R_2$

$= \frac{1.25 + 1.25R_2}{R_1} + I_{\textrm{adj}}R_2$

$= \frac{1.25 + 1.25R_2}{R_1} + \frac{I_{\textrm{adj}}R_1R_2}{R_1}$

$= \frac{1.25 + 1.25 R_2 + I_{\textrm{adj}}R_1R_2}{R_1}$

$= \frac{1.25 + R_2(1.25 + I_{\textrm{adj}}R_1)}{R_1}$ .

Now, solving for $R_2$ ...

$V_{\textrm{out}} = \frac{1.25 + R_2(1.25 + I_{\textrm{adj}}R_1)}{R_1}$

$R_1V_{\textrm{out}} = 1.25 + R_2(1.25 + I_{\textrm{adj}}R_1)$

$R_1V_{\textrm{out}} - 1.25 = R_2(1.25 + I_{\textrm{adj}}R_1)$

$R_2 = \frac{R_1V_{\textrm{out}}}{1.25 + I_{\textrm{adj}}R_1}$ .

**embob** · February 15th 2010, 03:39 AM

Thank you!

Do you know any good tutorials for rearranging equations. I could do with going through a couple of hundred examples...

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