题目

    Here is your best chance to travel around the UK in 2013: More than 200 B&Bs（bed & breakfast）across England, Scotland, Wales and Northern Ireland are selected to offer you amazing services for your stay at their lowest prices! Don’t miss it. Just collect the vouchers（活动券）in our B&B Daily printed from 01/04/2013 to 07/04/2013 and book the stays for your travel following the terms and conditions below: ●         The offer includes a room for the night and a breakfast the next morning. ●         The offer is of two kinds: ￡20 per 19．已知θ的终边过点（2，a），且$tan（\frac{π}{4}-θ）=-3$，则a=-4．