formula

$\langle \alpha x, y \rangle = \sum_{k=1}^n \alpha x_{k} \overline{y_{k}} = \alpha \sum_{k=1}^n x_{k} \overline{y_{k}} = \alpha \langle x, y \rangle \\ \langle x, \alpha y \rangle = \sum_{k=1}^n x_{k} \overline{\alpha y_{k}} = \overline{\alpha} \sum_{k=1}^n x_{k} \overline{y_{k}} = \overline{\alpha} \langle x, y \rangle$