Expert: Abe Mantell - 6/2/2009

Question
My name is David I am in grade 12

I do not understand Part A (1,2 and 3) on this page:
http://education.alberta.ca/media/930712/03%20pure30%20feb-09%20skydiving%20stud...


Answer
Hello David,

1. The vertex of the parabola is at (0,11), so we can write the
-  equation as y=a(x-0)^2 + 11, as for "a"...we know that when
-  y=0, x=3...so: 0=a(3)^2 + 11, so a=-11/9
-  Thus, y=-(11/9)x^2+11

2. Moving the origin over 2 units to the left, is equivalent to
-  moving the parabola 2 units to the right...so the equation
-  would be y=-(11/9)(x-2)^2 + 11

3. set y=0 and solve for x:
-  0-12250 = -(4.9/62500)x^2 ==> x^2 = 12250*62500/4.9
-  so x is 12500 ==> coordinates (12500, 0)

OK?  I hope this helps...

Abe