Multiplication by the complex conjugate :
mult_c_conjugate

mult_c_conjugate takes as argument an complex expression.
If this expression has a complex denominator, mult_c_conjugate multiplies the numerator and the denominator of this expression by the complex conjuguate of the denominator.
If this expression has not a complex denominator, mult_c_conjugate multiplies the numerator and the denominator of this expression by the complex conjuguate of the numerator.
Input :

mult_c_conjugate((2+i)/(2+3*i))

Output :

(2+i)*(2+3*(-i))/((2+3*(i))*(2+3*(-i)))

Input :

mult_c_conjugate((2+i)/2)

Output :

(2+i)*(2+-i)/(2*(2+-i))