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I'm trying to solve for two unknowns with two equations as follows;

Solve[{-161.2035 + 2.7 s - 2.7 a + 0.0039123 s^4 - 0.000567 a^4 = 
   0, -78.021525 + 0.01134 a^4 - 2.7 s - 2.7 a - 0.0035721 s^4 = 
   0}, {a, s}]

When I use this as the input it is just giving me the same as the output.

I've tried instead putting in {a}, {s} instead of together and it did exactly the same thing.

I've also tried using SolveAlways instead of Solve and there was no output returned at all.

I'm pretty new to Mathematica, so any help would be hugely appreciated!!

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  • 2
    $\begingroup$ Try Solve[{-161.2035 + 2.7 s - 2.7 a + 0.0039123 s^4 - 0.000567 a^4 == 0, -78.021525 + 0.01134 a^4 - 2.7 s - 2.7 a - 0.0035721 s^4 == 0}, {a, s}] $\endgroup$ – dr.blochwave Mar 16 '15 at 7:49
  • $\begingroup$ See here for the difference between = ("Set") and `==" ("Equal") reference.wolfram.com/language/tutorial/Equations.html $\endgroup$ – dr.blochwave Mar 16 '15 at 7:55
  • $\begingroup$ Thanks for the clarification! Definitely not giving me the answer I expected so I'll have to have another look through my equations. Thanks :) $\endgroup$ – Kirsty Mar 16 '15 at 7:58
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After replacing "=" by "==" and Solve by NSolve everything is fine. Have a look:

 eq1 = -161.2035 + 2.7 s - 2.7 a + 0.0039123 s^4 - 0.000567 a^4 == 0;
eq2 = -78.021525 + 0.01134 a^4 - 2.7 s - 2.7 a - 0.0035721 s^4 == 0;
NSolve[{eq1, eq2}, {a, s}]

(*   {{a -> 12.7656, s -> -15.9596}, {a -> -0.781212 + 12.0381 I, 
  s -> 1.55315 - 14.6168 I}, {a -> -0.781212 - 12.0381 I, 
  s -> 1.55315 + 14.6168 I}, {a -> -11.2011, 
  s -> 12.8086}, {a -> 12.8117 - 0.0417194 I, 
  s -> 0.737203 - 15.2581 I}, {a -> 12.8117 + 0.0417194 I, 
  s -> 0.737203 + 15.2581 I}, {a -> -0.831677 + 11.9915 I, 
  s -> -15.2949 - 0.669614 I}, {a -> -0.831677 - 11.9915 I, 
  s -> -15.2949 + 0.669614 I}, {a -> -0.823847 + 12.0818 I, 
  s -> 13.6774 + 0.842965 I}, {a -> -0.823847 - 12.0818 I, 
  s -> 13.6774 - 0.842965 I}, {a -> -11.1589 + 0.0495376 I, 
  s -> 0.911922 - 13.781 I}, {a -> -11.1589 - 0.0495376 I, 
  s -> 0.911922 + 13.781 I}, {a -> 12.8489, 
  s -> 14.4852}, {a -> -0.871665 + 12.046 I, 
  s -> 0.0643786 + 14.4434 I}, {a -> -0.871665 - 12.046 I, 
  s -> 0.0643786 - 14.4434 I}, {a -> -11.1023, s -> -14.6324}}  *)

NSolve should be used here, since the factors are anyway inexact. Have fun!

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