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Re: I need some help about this error


Plot have property of  HoldAll

In[58]:=
Attributes[Plot]
Out[58]=
{HoldAll, Protected}

So if you plot t={2x+1,-2x+3} with the next sentence,

t={2x+1,2x-3};
Plot[t,{1,2}]

error is returned. Plot uses to number 1 to evaluate "t".
But t is not a list of function, but only a letter. This happens
because of the Plot's property of HoldAll. Mathematica 
regard t as a letter "t", not a list of functions {2x+1,2x-3}

You can have mathematica know "t" as a list of function,
by using Evaluate in a Plot command.

t={2x+1,2x-3};
Plot[Evaluate[t], {x,1,2}] 

Help of Plot  and A4.2 might be useful to you.

************
milkcart
milkcart at m17.alpha-net.ne.jp









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