what number is -1.938E -6? i keep getting it in my graphing calculator whenever i get the minimum of the parabola. *im doing my Algebra 2 homework*

It sounds like just a rounding error. Should be zero, but something got rounded off a tiny bit in the equation.

You actually get a point on the curve where the line tangental to the curve has a slope of 0. The only place a slope of the tangent line is 0 on a curve is where it changes directions. You can also tell if the curve is ascending or decending at a give point using the first derivative. Calculus is awesome like that. Finding the first derivative is easy too. For example, the derivative of y=x^2 is y'=2x and the first derivative of y=x^3 is y'=3x^2 while the derivative of any constant is 0.