solve(eqn,x) giving wrong answer

Hello,

I am working with some polynomials and am solving for x and unfortunately I am not getting the correct answer which is really baffling. You can run it to get the answer, but if you take both solutions and work backwards for some value of x and y they are not correct. I was wondering if maybe my use of FloatingPointOutput is the issue?

sympref('FloatingPointOutput',true)

ans = logical
   0

syms x y

eqn = -1.5960e-06*x^2 + 0.0367*x - 2.0468 == y

eqn = 

 
solx = solve(eqn,x)

solx = 

I plugged this same formula into symbolab.com and got the correct answer (0.00133... is truncated but I confirmed the first one is the correct answer)

Not sure what's going on here...

Thanks!

Answer 1

[Cris LaPierre]

It looks the same to me. Just do the algebra.

b = -0.0367;
d = 0.000003192;
% Note that these values match what MATLAB is giving you
your_R1Coeff1 = -b/d

your_R1Coeff1 = 1.1497e+04

your_R1coeff2 = 1/d

your_R1coeff2 = 3.1328e+05

Answer 2

[Steven Lord]

You can check the answer.

sympref('FloatingPointOutput',true)

ans = logical
   1

syms x y
eqn = -1.5960e-06*x^2 + 0.0367*x - 2.0468 == y

eqn = 

solx = solve(eqn,x)

solx = 

simplify(subs(eqn, x, solx))

ans = 

leftside = lhs(eqn)

leftside = 

simplify(subs(leftside, x, solx))

ans = 

Looks right to me.