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Re: Parametric Solving Question From 14 Year Old


Hi Alan,

I don't have access to Mathematica right now, so I'm going to answer 
this from memory. I think you want to use the function Solve[], or 
its numerical analog, NSolve[]. Something along the lines of

Solve[ { x == 15*t*Cos[60*Degree],
          y == 15*t*Sin[60*Degree]-9.80665/2*t^2,
          y == 0 }, {x, t} ]

which tells Mathematica to solve for the variables x and t. 
Incidentally, I suspect you meant 60 degrees, so it's important to 
have the Degrees constant inside the trig functions, because Sin[] 
and Cos[] assume their arguments to be in radians. Actually, I'm not 
sure now whether its correct name is Degree or Degrees.

Hope this helps.
Wagner

At 2:44 AM -0400 on 5/16/00, Alan wrote:

>Hello!
>     I am 14 and am wondering how to solve parametric equations directly
>without graphing in Mathematica? I am figuring out when a projectile in
>motion hits the ground only due to the even force of gravity acting upon
>it. The parametric equation is:
>
>x(t)=15*t*Cos[60]
>y(t)=15*t*Sin[60]-9.80665/2*t^2
>
>I want to find the value x(t) and t when y(t)=0.
>
>         Thank you,
>         Alan



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