Mathematica Plotting Mathematica f[r_][x_]: Solving Derivatives & Plotting Lines

AI Thread Summary
The discussion focuses on plotting the function f[r][x] = 1 + r*x + x^2 and its derivatives in Mathematica. Users are trying to differentiate between solid and dashed lines based on the sign of the derivative. The conversation includes attempts to simplify the code by eliminating unnecessary tables and using the Solve function to find critical points. There is a request for a method to automate the definition of g[r] as functions without manual input. The overall goal is to enhance the plotting of the function while visually distinguishing the behavior of its derivatives.
Dustinsfl
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Code:
f[r_][x_] := 1 + r*x + x^2;
A = Table[
   cps[r_] = x /. Quiet[Solve[f[r][x] == 0, x], Solve::ratnz], {r, -5,
     5, 0.01}];

I want to then tell mathematica to check the derivative of f with each value from the table, plot the values, but make the lines where there derivative in less than 0 solid and dashed for greater than 0.

Any ideas on how to finish this?
 
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dwsmith said:
Code:
f[r_][x_] := 1 + r*x + x^2;
   cps[r_] = x /. Quiet[Solve[f[r][x] == 0, x], Solve::ratnz]

I want to then tell mathematica to check the derivative of f with each value from the table, plot the values, but make the lines where there derivative in less than 0 solid and dashed for greater than 0.

Any ideas on how to finish this?

So I got rid of the table.
Code:
f[r_][x_] := 1 + r*x + x^2;
cps[r_] = x /. Quiet[Solve[f[r][x] == 0, x], Solve::ratnz];
g[r_] = x /. Quiet[Solve[f[r][x] == 0, x], Solve::ratnz]
Plot[g[r], {r, -5, 5}, PlotStyle -> {Red, Thick}]
{1/2 (-r - Sqrt[-4 + r^2]), 1/2 (-r + Sqrt[-4 + r^2])}
Manipulate[Plot[f[r][x], {x, -4, 4}], {r, -10, 10}]

y[r_] = 1/2 (-r - Sqrt[-4 + r^2]);
t[r_] = 1/2 (-r + Sqrt[-4 + r^2]);
Plot[{y[r], t[r]}, {r, -5, 5}, 
 PlotStyle -> {{Dashing[{Medium}], Red}, {Thick, Red}}]

I can create what I want be defining the g[r] output but is there a way to have the g[r] output automatically defined as functions without doing it by hand?
 

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