Need some help with an odd output with solve

Hello, first time asking a question here. I am having a bizarre output when I try to use solve, and would like some help.

Here is the code:

syms x
eqn = (1315.2/(8.22-x))+(895.4/(2.42-x))+(240/(1-x))+(9.45/(0.378-x))+(0.75/(0.15-x))==800;
solx=solve(eqn,x)

And here is the output:

solx =

                                                                                                             0
   root(z^4 - (2273*z^3)/250 + (63332491*z^2)/4000000 - (1367320551*z)/200000000 + 721613169/1000000000, z, 1)
   root(z^4 - (2273*z^3)/250 + (63332491*z^2)/4000000 - (1367320551*z)/200000000 + 721613169/1000000000, z, 2)
   root(z^4 - (2273*z^3)/250 + (63332491*z^2)/4000000 - (1367320551*z)/200000000 + 721613169/1000000000, z, 3)
   root(z^4 - (2273*z^3)/250 + (63332491*z^2)/4000000 - (1367320551*z)/200000000 + 721613169/1000000000, z, 4)

I don't know if it's a problem with the code, or with my computer, but I'm unsure of what the z's in the solution correlate to. I'm also wondering if I can output the solution as just numbers, rather than these roots.

Thank you for answering, in advance.

Answer 1

[Star Strider]

Use the vpasolve function to get numerical output:

syms x
eqn = (1315.2/(8.22-x))+(895.4/(2.42-x))+(240/(1-x))+(9.45/(0.378-x))+(0.75/(0.15-x))==800;
solx=vpasolve(eqn,x)

solx =

                                    0
    0.1585817446596710456915191570641
   0.41963427877318302442907239553912
    1.5592338740562100917600813995941
    6.9545501025109358381193270478027

[John BG]

Why are you ignoring the imaginary part of the solution in the question?

The z in the answer is telling that the solutions have imaginary components.

You already have the answer, just to translate from symbolic to numerical:

vpa(solx)
ans =
                                                                           0
  0.1585817446596710456915191570641 + 5.4049015967984410970242199180548e-40i
 0.41963427877318302442907239553912 - 6.0171382378517158407579368645247e-40i
  1.5592338740562100917600813995941 + 3.0611832052663737186685847323496e-41i
  6.9545501025109358381193270478027 + 3.0611832052663737186685847323496e-41i

If you find this answer of any help solving your question,

please click on the thumbs-up vote link,

thanks in advance

John

[e-mail]

[Star Strider]

Interesting that vpasolve returned different results than vpa(solx). The imaginary parts are vanishingly small, and likely the result of computational inaccuracies.

Answer 2

[Walter Roberson]

double(solx)

Or,

solx = solve(eqn, x, 'MaxDegree', 4)

but be warned this is going to give you quite long solx.

Answer 3

[Shashwat Singh]

(((80000000*root(z^6 - (16200801*z^4)/10000 + 16924119873732035442801/40000000000000000, z, 1)^2)/160801 - (800000000000*root(z^6 - (16200801*z^4)/10000 + 16924119873732035442801/40000000000000000, z, 1)^4)/2605105001601 + 8000)*((40000000000*root(z^6 - (16200801*z^4)/10000 + 16924119873732035442801/40000000000000000, z, 1)^4)/2605105001601 - (4000000*root(z^6 - (16200801*z^4)/10000 + 16924119873732035442801/40000000000000000, z, 1)^2)/160801 + 40401/100))/(((40000000000*root(z^6 - (16200801*z^4)/10000 + 16924119873732035442801/40000000000000000, z, 1)^4)/2605105001601 - (4000000*root(z^6 - (16200801*z^4)/10000 + 16924119873732035442801/40000000000000000, z, 1)^2)/160801 + 40401/100)^2 - (40401*((1000000000*root(z^6 - (16200801*z^4)/10000 + 16924119873732035442801/40000000000000000, z, 1)^4)/2605105001601 - (100000*root(z^6 - (16200801*z^4)/10000 + 16924119873732035442801/40000000000000000, z, 1)^2)/160801 + 10)^2)/25)^(1/2)