Why does the quadratic formula work all the time

Which function families have maximums and minimums? 1.)linear absolute value functions and exponential functions 2.) linear absolute value functions and quadratic functions 3.) linear absolute value functions and linear functions 4.) linear absolute value functions and constant functions

Find the roots of the equation below. x^2 - 6 + 9 = 0

Which is f(5) for the function –2x2 + 2x - 3?