\displaystyle\sum_{\left\lbrace i:1\le i\le n\right\rbrace\backslash\left\lbrace j_1,\dots,j_k\right\rbrace}\mu_i\,r_i+\sum_{l=1}^k\Re(\mu_{j_l})\,r_{j_l}=-\imath\,\sum_{l=1}^k\Im(\mu_{j_l})\,r_{j_l}