See this: http://i.imgur.com/VtJVa.png Construct a parabolic equation based off of this.

Question

anonymous · Answer

I got $$\frac{-1}{640}x^2=y$$

anonymous · Answer

The book says it is right. The problem comes when doing part 2. "How far from the center of the road is the road surface 0.1 foot lower than in the middle?"

anonymous · Answer

I plug in -.3 for y and I don't get 8, the answer.

anonymous · Answer

$$-640(-.3)=x^2 ~\therefore ~ x^2=192\therefore x=8\sqrt{3}$$

anonymous · Answer

I find plugging -.1 in works.

experimentx · Answer

y(x) = -(x - 16)(x+16)/640 http://www.wolframalpha.com/input/?i=plot+y%28x%29+%3D+-%28x+-+16%29%28x%2B16%29%2F640

experimentx · Answer

also try shifting the origin by putting x = x - 16 or x = x + 16

anonymous · Answer

Why didn't it work before?

experimentx · Answer

i don't know ... did the above formula work??

anonymous · Answer

The equation I derived at the beginning was said to be right. It just didn't work for part 2.

anonymous · Answer

Why would horizontally shifting do the trick?

experimentx · Answer

http://www.wolframalpha.com/input/?i=plot+y%28x%29+%3D+-%28x+-+16%29%28x%2B16%29%2F640%2C+y%28x%29+%3D+-x%5E2%2F640

experimentx · Answer

i didn't know if you wanted this http://www.wolframalpha.com/input/?i=plot+y%28x%29+%3D+-%28x+-+32%29%28x%29%2F640

anonymous · Answer

So what you did was shift it up vertically?

anonymous · Answer

That's it?

experimentx · Answer

seems that way

anonymous · Answer

Thank you.

experimentx · Answer

yw