How to convert {x -> 4} to simply 4?

Asked May 22 '19 at 20:09

Active May 22 '19 at 20:22

Viewed 43 times

I am using the Solve function to obtain two solutions for a quadratic, then I want to use those two solutions as input for something else but I can't because they are in the form of (x->number}

potential = 5/2*x^2
solut2 = Part[Solve[potential == 40, x], 2]

The output that comes out is

{x -> 4}

but I need simply 4 to be the input in some other functions. Thank for your help!

edited May 22 '19 at 20:22

David G. Stork

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asked May 22 '19 at 20:09

Mattia

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Solve and its kin returns lists of Rules and those are meant to be used with Replace, e.g. as in x /. Solve[potential == 40, x][[2]]. – Henrik Schumacher May 22 '19 at 20:10
Part[...,2] $\to$ Part[..., 2, 1, 2]. – AccidentalFourierTransform May 22 '19 at 20:10
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Possible duplicate: https://mathematica.stackexchange.com/questions/18393/what-are-the-most-common-pitfalls-awaiting-new-users, esp. https://mathematica.stackexchange.com/a/18706/4999 – Michael E2 May 22 '19 at 20:20

How to convert {x -> 4} to simply 4?

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