—Hi, Kate. You are riding a bike today. —Yes, driving a car to school every day makes me much ______. A. fat B. fatter C. thin D. thinner 答案:B如图,四棱锥P-ABCD中,底面ABCD为菱形,PA⊥底面ABCD,AC=2,PA=2,E是PC上的一点,PE=2EC.
(Ⅰ)证明:PC⊥平面BED;
(Ⅱ)设二面角A-PB-C为90°,求PD与平面PBC所成角的大小
【解析】解法一:因为底面ABCD为菱形,所以BDAC,又