quadratic formula values

[Emily Tieu 2K]

How do we know which x-value to choose from when both are positive values after computing the quadratic formula?

[Simrah_Ahmed1J]

If you've solved the equation right and there's two positive x values as a result, there should be one x value that is greater even than the initial concentration itself, and we know that would have to be wrong because if we're using it as a change we cant have the equilibrium concentration be negative.
So in short: the x value that is greater than the initial concentration is not the correct one.

[Sofia Azmat 1I]

When you have two positive values, I believe you pick the value that is less than what you see when you look at the initial concentration of the reactants, and reject the value that is greater than the initial concentration of the reactants.

[Catie Donohue 2K]

I believe Dr Lavelle said that you take that value that is smaller than the initial concentrations of reactants, because it wouldn't make sense for a product to increase by that higher X amount when there aren't enough reactants available to complete that reaction.

[Adrienne Chan 1G]

Even though they both might be positive, Lavelle said only one of them will make sense when they're plugged into the equilibrium values. I just plug them into all of the values in the "E" row of the ICE table and it's always given me the right answer.

[vuongnaomi1L]

if both are positive, choose the one that will not result in a negative number when you plug it in the equations for equilibrium constants. For example, if an equation to find the equilibrium concentration of a reactant is 0.5-x and you have values 0.2 and 0.8 from your quadratic equation, 0.8 will result in a negative concentration, so you would pick 0.2.

[Lily Anne Garcia 1C]

no negative x values and if theyre both positive one will be bigger than the initial condition which isnt right

[Teti Omilana 1G]

You shouldn't choose the one that is negative or that is too big to make sense in the context of the problem.

[David Liu 1E]

even though both are positive, only one should make sense given the conditions of the question

[Yeonjoo Kim 2B]

You have to choose the positive x-value! If they're both positive, then you should try to plug them in to see if one of them results in a negative value.

[jia207]

You would use the positive value for the answer to the question. If both are positive, choose what value makes sense for the question.

[James Fu 2F]

If there is one negative and one positive, only the positive one makes sense.

If they are both positive, only one of them should make sense so you'd find the pH and rule out the one that doesn't make sense.

[RaniyaFeroz_1E]

Try subtracting them from the initial molarity. If you get a negative output, then that one is not the correct answer.

[LeahSWM 2E]

always go with the positive when presented with a negative and a positive. if both are positive you'll have to use both in further steps and see which one gives you a negative value.