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### 11.59

Posted: Tue Jan 15, 2019 9:59 pm
After using the quadratic to solve for x, how do we know which outcome is valid if both numbers are positive?

### Re: 11.59

Posted: Tue Jan 15, 2019 10:02 pm
To check, you can plug the two x values back into the ICE table. In cases like this, usually when you plug in the larger x value, it results in the equilibrium concentrations of both reactants being less than 0, which cannot happen.

### Re: 11.59

Posted: Tue Jan 15, 2019 10:06 pm
If you plug in the larger positive x value, you will find that the equilibrium concentrations of the reactants are negative, and that is not possible, meaning that value can be disregarded. Therefore, there would be only one valid x value.

### Re: 11.59

Posted: Tue Jan 15, 2019 10:12 pm
For the two options, if both are positive, plug it into the ICE table and make sure that your equilibrium concentration is still positive. If x is too large then this will be negative which cannot happen. In any case, it is good to check both solutions if unsure, especially if both are positive values.