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I spent quite some time trying to figure out why my answer was wrong, only to discover that it was right, just simplified in a way a very poor way in Mathematica:

vs1 = (1. (3.3 + 1. I4 R1 + 1. I4 R2) Rs)/(1. R1 + 1. R2 + 1. Rs)
vin1= (3.3*R1+vs1*R2)/(R1+R2)//Together//FullSimplify

which results in $vin1$: $$=\frac{3.3 (1. R1^2 + 1. R1 R2 + 1. R1 Rs + 1. R2 Rs + 0.30303 I4 R1 R2 Rs + 0.30303 I4 R2^2 Rs)}{((R1 + R2) (1. R1 + 1. R2 + 1. Rs))}$$

This can be reduced to: $$vin1 = \frac{(3.3 R1+3.3 Rs+1. I4 R2 Rs)}{(1. R1+1. R2+1. Rs)} ,$$ but I can't get Mathematica there. I've tried //FullSimplify, //Together, //Cancel //Factor, etc. and I cannot figure out how to have Mathematica fully simplify the resulting expression for vin1.

Thanks for the help.

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1 Answer 1

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Is

N@Simplify@Rationalize@vin1
(* (0.1 (33. R1 + (33. + 10. I4 R2) Rs))/(R1 + R2 + Rs) *)

what you are looking for? Finite precision numbers may be confusing Simplify.

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  • $\begingroup$ Thank you!! Can you explain what exactly this statement is doing (and why it works)? Thanks again! $\endgroup$
    – jrive
    Apr 24, 2019 at 14:54
  • $\begingroup$ @jrive, Rationalize converts all decimal numbers to rational numbers, after which Simplify performs the desired simplification. Finally, N coverts the rational numbers back to decimal numbers. Omit N@, if you are satisfied with an answer containing only rational numbers. In my experience, Mathematica generally works better with rational numbers. Thanks for accepting my answer. $\endgroup$
    – bbgodfrey
    Apr 24, 2019 at 15:14
  • $\begingroup$ I wonder now if all my struggles with simplifying results in the past could have been avoided by rationalizing!! Thanks! $\endgroup$
    – jrive
    Apr 24, 2019 at 15:25

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