what is (v3)/3?

it must be 0 for having two inflection points that are the same but different in sign.

because for being an inflection point, the second derivative must be zero. which means that 12ax^2+6bx-2c=0

if you substitute (v3)/3 and -(v3)/3 for x and subtract the second equation from the first, you will have: 12b((v3)/3)=0. which indicates whether b or v3 are 0.

I don't have any idea what is v3. Is it another variable?