solve() returns the symbol not the solution

Question

Ryan Good 2015-3-15

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https://ww2.mathworks.cn/matlabcentral/answers/183303-solve-returns-the-symbol-not-the-solution

评论： Star Strider 2015-3-16

I am trying to use solve() and it does not seem to be working. It keeps returning the symbol I am solving for, not a solution. I tried using sample code from the documentation and it still gives the same answer.

syms a b c x

eqn = a*x^2 + b*x + c == 0;

solx = solve(eqn, x)

solx =

x

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Answer 1

Star Strider 2015-3-15

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It returns exactly what it should:

solx =
   -(b + (b^2 - 4*a*c)^(1/2))/(2*a)
   -(b - (b^2 - 4*a*c)^(1/2))/(2*a)

If you want a numeric answer, you have to supply numeric values for ‘a’, ‘b’, and ‘c’. (You might also want to use the vpasolve function if you want a strictly numeric result.)

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Ryan Good 2015-3-16

What I posted was copy and pasted from the documentation, there is no mistake in Eqn. The answer is the last line , solx = x. I did not get the -(b + (b^2 - 4*a*c)^(1/2))/(2*a) answer as Star returned.

It seems I must have a problem with the symbolic package. MuPad is missing as well.