Math
posted by Sophie .
An engineer is desingning a parabloic arch, the arch must be 15 m high , and 6 m wide, at a height of 8 m
a) determine a quadratic fundtion that satisfies these conditions
b) what is the width of the arch at its base

Let the arch be centered on the yaxis. Then the equation will be
y = ax^2 + k
It will have height 6 at x = 3 and 3
The vertex will be at (0,15)
y = ax^2 + 15
6 = a(3^2) + 15
6 = 9a + 15
9 = 9a
a = 1
y = x^2 + 15
y=0 when x^2 = 15, so the width is 2√15 at its base 
Roof of a tunnel is in the shape of parabolic arch whose highest point is 18m above a road. The road surface is 16m wide at ground level. Lights are placed in the tunnel 12 m high. How far from the center of the tunnel are the lights placed?