Why the first term of the quadratic equation should be positive?

Question

For example -3x^2+5x+8 

 

According to my teacher the first time should be positive. Why?

Answer 1

There is no reason the first term should be positive in a quadratic polynomial

of form ax²+bx+c = d.

 

If the coefficient of the square term is negative, it means that the graph will be a

parabola opening downward with the vertex being a maximum.  if the coefficient

of the square term is positive, the graph will be a parabola opening upward with

the vertex being a minimum.

 

Bear in mind, you have not provided a "quadratic equation."  Your example is an

expression.  In order to be an "equation" it requires an equal sign.