题目

How to improve our memory?As we grow older, cognitive(认知的)conditions tend to affect our brain's memory functions, often robbing us of its most important uses. And we don't even have to reach old age to lose it. Thankfully, we don't have to sit around and just let our brains slip away, since we can easily be proactive and help keep it as sharp as ever.【1】Sharpen your brain with mnemonic devices---Mnemonic devices(助记设备)are techniques that a person can use to help them retain information better. 【2】. This is because it essentially acts like brain training and forces it to wo如图，点E（0，4），O（0，0），C（5，0）在⊙A上，BE是⊙A上的一条弦．则tan∠OBE=    ．