Get one equation from two complex roots

Hi, I would like to ask if it is possible to get a single equation from this expression (s-(-9+j*3))*(s-(-9-j*3)).

I tried to use syms s (to declare s as a variable) but I only get a simplified form of this expression which is (s+9-j*3))(s+9+j*3)) as the answer.

I calculated by hand that the equation in the end should be s^2+18*s+90.

Thank you.

Answer 1

[KSSV]

syms s 
eqn =  (s-(-9+1i*3))*(s-(-9-1i*3)) ;
simplify(eqn)

ans = 

Answer 2

[John D'Errico]

You can use

help sym/expand

 EXPAND Symbolic expansion.
    EXPAND(S) writes each element of a symbolic expression S as a
    product of its factors.  EXPAND is most often used on polynomials,
    but also expands trigonometric, exponential and logarithmic functions.
 
    EXPAND(S,'ArithmeticOnly',true) limits expansion to basic arithmetic,
    whereas EXPAND(S,'ArithmeticOnly',false) (which is the default) will
    also expand trigonometric and other special functions.
    
    EXPAND(S,'IgnoreAnalyticConstraints',VAL) controls the level of 
    mathematical rigor to use on the analytical constraints while simplifying 
    (branch cuts, division by zero, etc). The options for VAL are TRUE or 
    FALSE. Specify TRUE to relax the level of mathematical rigor
    in the rewriting process. The default is FALSE.
 
    Examples:
       syms x y
 
       expand((x+1)^3)   returns  x^3+3*x^2+3*x+1
       expand(sin(x+y))  returns  sin(x)*cos(y)+cos(x)*sin(y)
       expand(exp(x+y))  returns  exp(x)*exp(y)
       expand((exp(x+y)+1)^2,'ArithmeticOnly',true)
                         returns  exp(2*x + 2*y) + 2*exp(x + y) + 1
       expand(log(x*y))  returns  log(x*y)
       expand(log(x*y),'IgnoreAnalyticConstraints',true)
                         returns  log(x)+log(y)
 
    See also SYM/SIMPLIFY, SYM/FACTOR, SYM/COLLECT.

    Documentation for sym/expand
       doc sym/expand

to force MATLAB to expand an expression that contains parens.

syms s
expand((s-(-9+i*3))*(s-(-9-i*3)))

ans =