For the answer to the question above,
diameter 200 means x-intercepts - 100 and 100
maximum height = 50 means y-vertex = 50
y = ax^2 +c
c=50
y =ax^2 + 50
and
ax^2 + 50 = 0 for x = + 100 and x = -100
10000a + 50 = 0
a = - 50/10000
a = -5/1000 = - 0.005
my answer is
y = - 0.005 x^2 + 50
