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I need to find all the roots of this function. I know it is simple to find by hand, however, I wish to learn how to do it so I can apply it later. The problem is that it only gives me one root.

Distance[t_] := t*(t - 1)*(t - 1.5)^2*(t - 3)
Velocity[t_] := Simplify[Distance'[t]]
FindRoot[Velocity[t], {t, -100, 100}]

{t -> 2.63641}

I can find the minimum and maximum. However, how would I plot them on the same graph as the function without copy and pasting the points manually into a list?

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    $\begingroup$ Any reason you can't just use Solve[Velocity[t] == 0, t]? $\endgroup$
    – Andy Ross
    Nov 14, 2012 at 22:21
  • $\begingroup$ Gah! You might as well close the question now. $\endgroup$
    – General Stubbs
    Nov 14, 2012 at 22:32

1 Answer 1

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As Andy said, you can simply use

solutions = Solve[velocity[t] == 0, t]

to find the extrema: {{t -> 0.291169}, {t -> 1.17242}, {t -> 1.5}, {t -> 2.63641}}

To answer the second part of your question:

However, how would I plot them on the same graph as the function without copy and pasting the points manually into a list?

You can use Show to draw multiple plots or graphics in the same coordinate system:

Show[
 Plot[distance[t], {t, 0, 3}],
 Graphics[{Red, PointSize[Large], 
   Point[{t, distance[t]} /. solutions]}]]

Result:

Mathematica graphics

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  • $\begingroup$ You could also use Epilog to plot the points. $\endgroup$
    – wxffles
    Nov 14, 2012 at 23:06
  • $\begingroup$ Thank you so much. When I find the maximum and minimum, I'll just define it as a variable. $\endgroup$
    – General Stubbs
    Nov 15, 2012 at 0:52

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