If the graph of the quadratic function y = a x 2 + b x + c crosses the x-axis, the values of x at the crossing points are the roots or solutions of the equation a x 2 + b x + c = 0.

Second, it gives you uncertainties in the coefficients of the fitting function. Plot 0.997: I call it Plot 0.997 because if you just do a google search for Plot you will never find it.