Question 70792
Pick some x-values that will help you. The best ones are 
x = 0
x = +1
x = -1
Then compute the y-value that goes with each x-value
In this case,
x = 0, y = -15
x = +1, y = 70
x = -1, y = 44
The y-intercept is -15 as you can see
To find the x-intercept, make y=0 and find x
with the quadratic formula
{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}
this gives you 2 values for x because of the +/- in front
of the square root
Your equation is in the form {{{y = ax^2 + bx + c}}}
a = 72
b = 13
c = -15
The vertex will be the value which is exactly between
the the x-values that make y=0, and that is {{{-b/2a}}}