Question 103470
a general equation for the parabola is (x-h)^2=4p(y-k)
where the vertex is located at (h,k) and p is the distance from vertex to focus


designating the bottom of the reflector as the origin (0,0); and letting 1 unit=40 cm makes the ends of the diameter (1,1) and (-1,1)


(x-0)^2=4p(y-0)^2 ... x^2=4py^2 ... 4p=x^2/y^2 ... 4p=1/1 ... 4p=1 ... 4p=40cm ... p=10 cm


10 cm from the vertex is 30 cm from the opening