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Manipulate[
 Plot[a x^2 + b x + c, {x, -10, 10}, PlotRange -> {-50, 50}, 
  PlotLabel -> Row[{a x^2 + b x + c = y}]], {{a, .1}, -10, 10, 
  Appearance -> "Open"}, {{b, .1}, -10, 10, 
  Appearance -> "Open"}, {{c, .1}, -10, 10, Appearance -> "Open"}]

Then I am having this after evaluating:

Set::write: Tag Plus in 0.1 +0.1 x+0.1 x^2 is Protected.

What does this mean?

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  • $\begingroup$ You have a basic syntax error in your PlotLabel option. $\endgroup$
    – dionys
    Commented Sep 20, 2015 at 16:58
  • $\begingroup$ To expand slightly on @dionys comment, you will want to enclose the equation you are using as a plot label in quotes to make it a string and prevent Mathematica from trying to evaluate it by assigning values to the left hand side. $\endgroup$
    – MarcoB
    Commented Sep 20, 2015 at 17:00
  • $\begingroup$ Other duplicates: (11868), (11982) $\endgroup$
    – Michael E2
    Commented Sep 20, 2015 at 20:08

1 Answer 1

1
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You have assign (=) instead of == in the:

{a x^2 + b x + c = y}

Just change this into and this will be fixed.

{a x^2 + b x + c == y}
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