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ForumsDiscussion Forum → Physics/Calculus problem
Physics/Calculus problem
2006-09-15, 12:05 PM #1
Hello, this is the first time I have ever asked for homework help here. Please, help.

I need to find the lowest slope of a line in order for it to intersect with a parabola.

If the parabola is, say, 2x^2+5, how would I determine the lowest slope of the line that intersects with it?
2006-09-15, 12:08 PM #2
A line can intersect with the parabola at any slope depending on its X and Y intercepts.

Can you provide a diagram?
2006-09-15, 12:16 PM #3
I don't have the software at the moment, but I will try to explain it more clearly.

The parabola is concave up, with the origin a certain number above (y) the origin, but the x value of the origin is 0.

The line intersects the origin. I want to determine the value of the slope which will intersect the parabola only once, on the right side of the origin (this will presumably be the lowest slope).
2006-09-15, 12:20 PM #4
It sure sounds to me like the line you want is y = 5, where the slope is zero.
2006-09-15, 12:21 PM #5
It would be nice, certainly, but the line must intersect the origin.
2006-09-15, 12:24 PM #6
....
2006-09-15, 12:31 PM #7
I want to find the slope of that line. Thanks for your help, by the way.
Attachment: 13977/Untitled.png (5,407 bytes)
2006-09-15, 12:39 PM #8
take the derivative of the parabola with respect to x and plug in your y value to rearange it into a y=mx+b format. what you are looking for is called a tangent line.
I'm not wearing any pants...
2006-09-15, 12:47 PM #9
Kanchi is exactly right.
nope.
2006-09-15, 12:49 PM #10
Plug in which Y value?

y=2x^2+5
y'=4x

Then?
2006-09-15, 12:52 PM #11
The slope must be 4x where x is the intersection between the parabola and the tangent line. You need to find the value for x where the tangent line intersects the origin.
2006-09-15, 1:10 PM #12
Ignore me.
nope.
2006-09-15, 2:57 PM #13
Got it, thanks all.

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