If we define $3v^2 = ab+bc+ca$, then doesn't that mean $3v^2$ must be positive due to the exponentiation and positive $3$?
I note that if for example $a = −1, b = −2, c = 3$ we get $3v^2 = −7$! I understand that the algebra is not tricking me but I am just not convinced that two positives multiply to form a negative.