### Quadratic

Posted:

**Thu Jan 16, 2020 9:53 am**What do you do if the after using the quadratic equation and you get two positive answers?

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=49&t=56403

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Posted: **Thu Jan 16, 2020 9:53 am**

What do you do if the after using the quadratic equation and you get two positive answers?

Posted: **Thu Jan 16, 2020 11:22 am**

You would test each value with the equilibrium expression that was found using the ICE table to see if the value is reasonable. Usually one of the values found using the quadratic equation will cause one of the concentrations to be negative, which is not possible.

Posted: **Thu Jan 16, 2020 11:24 am**

You should test each value, and rule out the one that is unreasonable in the situation. Usually you will end up with a positive and negative number, so it can immediately rule out.

Posted: **Thu Jan 16, 2020 11:27 am**

i don't think you would get 2 positive answers often, but just in case i'd plug the values back into the ICE table to see which value is more reasonable

Posted: **Thu Jan 16, 2020 11:28 am**

I think the chances that you would get two positive values after using the quadratic equation are pretty low but if you do I would plug them back into the ICE table and see which value is more reasonable.

Posted: **Thu Jan 16, 2020 11:48 am**

If you get two positive answers, you could rule out the value that is greater than your initial concentration since it would result in a negative number when plugged in to the equilibrium expression.

Posted: **Thu Jan 16, 2020 4:55 pm**

If you do the quadratic equation and get a positive and negative number would you just discredit the negative number? Why?

Posted: **Fri Jan 17, 2020 11:56 am**

If you use the quadratic formula and get two positive answers, you would choose the answer where if you subtract it from any of the initial conditions given it would be result in a reasonable and nonnegative concentration or pressure.

Posted: **Fri Jan 17, 2020 4:38 pm**

You would use the number that is less than your initial concentration you were given in the original problem.

Posted: **Fri Jan 17, 2020 5:02 pm**

You will test out the two answers and the answer that is less than the initial answer will be the correct one

Posted: **Fri Jan 17, 2020 5:12 pm**

Ruby Richter 2L wrote:If you do the quadratic equation and get a positive and negative number would you just discredit the negative number? Why?

Because you can't have a negative concentration