Question

In the assifnments from this course on the 1 problem set, in exercise 3 I simply dont understand what I'm doing wrong.
y = 1000 - x^2
y' = -2x
I need to find the line that is tangent to y and that also passes through (0,1100).
I get y-yo=y'(xo)(x-xo)
But i dont know (xo,yo)
Please help

Original question:
3. On the planet Quirk, a cell phone tower is a 100-foot pole on top of a green
mound 1000 feet tall whose outline is described by the parabolic equation y = 1000 − x^2
. An ant climbs up the mound starting from ground level (y = 0). At what height y does the ant begin to
see the tower?

Answer 1

There is a nice explanation of the method to solve this at this link: http://math.stackexchange.com/a/137068

The post I linked to has the solution, but it might be helpful to read a few other posts there. Even with that information, the solution might be difficult. I'll help you get there, if needed.

By the way, thanks for asking this question. I stumbled on this type of problem a few months back, and just couldn't crack it. That forum post I linked to helped a lot. And I did crack it. When you asked the question, that gave me an opportunity to see if I still remembered it. I vaguely did, but I had to refer back to that forum post lol.

Answer 2

Thanks a lot for the post. I just craked it. I'm really happy. It was really just a system because the tangent point belongs to both the tangent line and the curve :D thx a lot man!!

Answer 3

You're welcome.
Very true, I haven't tried to solve one that way. It did occur to me that setting it up as a system of equations might be easier than parameterizing a point on the curve.