某资料室在计算机使用中(如右图所示),编码以一定规则排列,且从左至右以及从上到下都是无限的.此表中,主对角线上数列1,2,5,10,17,…的第12项的值是____ ;编码100共出现____ 次.
(Ⅰ)证明:AC=AB1;
(Ⅱ)若AC⊥AB1,∠CBB1=60°,AB=BC,求二面角A﹣A1B1﹣C1的余弦值.
They usually spend two hours _______ their homework every day.