How can I find the curve (parabola) of best fit for the data attached without using a graphing calculator to instantly graph it. Is there a method I can use to come up with the equation of the parabola (i. e. polynomial regression, calculus?) Thank you so much!

Thanks for free points

check the picture below.

well, the angle at the vertex d is clearly not a right-angle, let's check for the one at the vertex f which does look like,   however if it's indeed, that means ef is perpendicular to df, in which case their slopes will be negative reciprocal of each other.

so the negative reciprocal of the slope of ef is 1, however the slope of df is not 1, is 1/2, so nope, they're not perpendicular lines.