—You've been in college for half a year. Are you familiar with your president?
—Yes. He is an outstanding leader who _____ his reputation.
A:looks out for
B:comes up with
C:lives up to
D:looks forward to
设A是由有限个正整数组成的集合,若存在两个集合B,C满足:
①B∩C=∅;
②B∪C=A;
③B的元素之和等于C的元素之和.
则称集合A“可均分”,否则称A“不可均分”.
(Ⅰ)判断集合M={1,3,9,27,…,3n}(n∈N*)是否“可均分”,并说明理由;
(Ⅱ)求证:集合A={2015+1,2015+2,…,2015+93}“可均分”;
(Ⅲ)求出所有的正整整k,使得A={2015+1,2015+2,…,2015+k}“可均分”
已知圆系方程(x﹣m)2+(y﹣2m)2=5(m∈R,m为参数),这些圆的公切线方程为____
设计一张折叠型方桌子如图,若AO=BO=50cm,CO=DO=30cm,将桌子放平后,要使AB距离地面的高为40cm,则两条桌腿需要叉开的∠AOB应为( )