$$ P_0 = \frac{E^2}{2R_L} $$
$$ E = \sqrt{P_0 \cdot 2 \cdot R_L} = \sqrt{2\cdot2\cdot8} = 4\sqrt{2}=5.656... \simeq 5.7 $$
$$ E = 5.65 + 2 = 7.65 \simeq 8[\rm{V}] $$
$$ P_0=\frac{E^2}{2R_L} = \frac{8^2}{2 \cdot 8} = 4[\rm{W}] $$
$$ i_{C6m} = \frac{E}{R_L} = \frac{8}{8} = 1 $$
【参考資料1】アナ電Ⅲ オペアンプ 設計書 C-8班 11ce577ee4e68000be3ece845f738014.html