求几个____的和,用乘法计算比较简便。
(Ⅰ)求证: BD⊥EG ;
(Ⅱ)求平面 DEG 与平面 DEF 所成锐二面角的余弦值.
42500000用科学记数法表示为 ____.
Have you the people here? It is said that they have a kind of strange illness.