- #1

MathTroubled

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## Homework Statement

Graph this equation:

P=-0.2t^3+2t^2+8t+2

t belongs to [0,13]

## Homework Equations

## The Attempt at a Solution

Can't seem to get factored to find x-int.

and the rest of the graph.

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- Thread starter MathTroubled
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- #1

MathTroubled

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Graph this equation:

P=-0.2t^3+2t^2+8t+2

t belongs to [0,13]

Can't seem to get factored to find x-int.

and the rest of the graph.

- #2

uart

Science Advisor

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Go ahead and find the start/end points plus any max/min and POIs in the given region.

- #3

MathTroubled

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Can anyone show me the steps they took to solve this?

- #4

Ray Vickson

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Can anyone show me the steps they took to solve this?

Have you never, ever, drawn a graph before?

RGV

- #5

MathTroubled

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yeah my textbook doesn't describe transformations well for this chapter.

- #6

Ray Vickson

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yeah my textbook doesn't describe transformations well for this chapter.

I did not ask about "transformations". I asked you if you had ever drawn a graph. Is the answer 'yes' or 'no'?

If you have already done similar things before, just do the same things for this problem.

If you have not drawn a graph before (and if your book does not explain how to do it) there are numerous web pages

that explain what to do. For example, see

http://cstl.syr.edu/fipse/grapha/unit2/unit2.html [Broken] and

http://www.cimt.plymouth.ac.uk/projects/mepres/book8/bk8i14/bk8_14i3.htm .

In your case, however, the curve y = f(t) is not a straight line, so all you can do is make a table of some(t,y) values, and

hand-draw a smooth curve that passes through them.

RGV

Last edited by a moderator:

- #7

Simon Bridge

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Stand back and look what shape it is trying to be and where it seems to be heading for the t axis. This will tell you when you are getting close to the roots.

Particularly - plot p for t=0 and t=13 (your endpoints). If your endpoints are on opposite sides of the t axis, then there is at least one root. If p is on opposite sides of the t axis for two adjacent values of t, then there is at least one root between them.

Use Newton-Raphson's method to get the rest of the way.

Looks like you can find and characterize the turning points of the graph OK ... that will also give you clues.

Or you can look up the general formula:

http://en.wikipedia.org/wiki/Cubic_function

- #8

SammyS

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If you shift the graph down by 2 you can factor that.## Homework Statement

Graph this equation:

P=-0.2t^3+2t^2+8t+2

t belongs to [0,13]

## Homework Equations

## The Attempt at a Solution

Can't seem to get factored to find x-int.

and the rest of the graph.

y = P(t) - 2 = -0.2t

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