If we know the roots (solutions) we can find the equation of the second-degree function using the formula above:

In this case, a = -1, x1 = 2 and x2 = 4. Therefore the equation will be:


The vertex is maximum (see that the function has a clear max value).
The solutions to the function are the roots (place in the x-axis where the function cross). They are 2 and 4.
The y-intercept is the point with the format (0,y). Thus to find this point we can substitute 0 into the function:


The y-intercept will be y = -8.