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Re: Any body can help me solve the equation with piecewise function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg87110] Re: Any body can help me solve the equation with piecewise function
  • From: Bill Rowe <readnews at sbcglobal.net>
  • Date: Tue, 1 Apr 2008 03:21:06 -0500 (EST)

On 3/31/08 at 2:04 AM, loveinla at gmail.com wrote:

>I have a problem to solve, but it seems not easy because of the
>piecewise function involved. I am wondering how we should deal with
>piecewise function when solving an equation or doing optimization.

>To give you an simple example, the piecewise function is f(x)= 3x if
>x<0; f(x)= 0 if x>=0. And I want to solve the equation f(x)+6=0.

>I actually define the piecewise function at first using "Which" and
>then try to use "NSolve" to solve it. However, NSolve doesn't work
>through.

>Anybody know how should I solve this kind of problem generally in
>Mathematica?

How about using Reduce? For example,

In[1]:= f[x_] = Piecewise[{{3 x, x < 0}, {0, x >= 0}}];

In[2]:= Reduce[f[x] + 6 == 0, x]

Out[2]= x == -2


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