What does it mean when the coefficient a in a quadratic regression model is zero?

Question

 I just need help on whether it is something I can put into the calculator because I have been working with my calculator a lot and if  I am correct whether or not it would be a straight line.

Answer 1

if a-0 in y=ax^2 + bx + c  then y = bx + c or, renaming it, y = mx + b (different "b"), so it's not quadratic, but a st. line.

 

Recommendation--plot (graph) the points first; if shape does not appear to be parabolic, don't choose quadratic regression..