matlab - Finding the points where a complex function is real-valued -

i have defined following complex system:

syms x  sys(x) = ((10+1.*i.*x))/(20+(5.*i.*x)+((10.*i.*x).^2))+((1.*i.*x).^3);  imaginarypart = imag(sys) 

matlab returned following results:

imaginarypart(x) =  - real(x^3) + imag((10 + x*1i)/(- 100*x^2 + x*5i + 20))   realpart(x) =  - real(x^3) + imag((10 + x*1i)/(- 100*x^2 + x*5i + 20)) 

now value of x imaginarypart(x) 0? (i.e. imaginarypart(x)= 0)?

as @andrasdeak commented, solve trick you:

s = solve(imaginarypart(x)== 0,x);