题目

Planning a visit to the UK? Here we help with ways to cut your costs. AVOID BIG EVENTS  Big sporting events, concerts and exhibitions can increase the accommodation and make it harder to find a room. A standard double room at the Thistle Brighton on the final Friday of the Brighton Comedy Festival (19, Oct.) cost £ 169.15 at Booking. Com. A week later, the same room cost £ 118.15. If you can be flexible and want to know dates to avoid ─ or you’re looking for a big event to pass your time ─ check out sites such as Whatsonwhen.com, which allow you to search for events in the UK b已知：如图，AB=3，AC=4，AB⊥AC，BD=12，CD=13，（1）求BC的长度；（2）证明：BC⊥BD．