Cho ΔABC có các cạnh AB=c, BC=a, AC=b, các góc được kí hiệu A, B, C, diện tích kí hiệu là S. Chứng minh $S=\frac{1}{2}ab.sinC=\frac{1}{2}ac.sinB=\frac{1}{2}bc.sinA$

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SAINT DAVID’S DAY Saint David is the patron saint of Wales. St. David was a Christian holy man and teacher. Saint David’s Day is celebrated on the first day of March every year, in remembrance of the anniversary of his death in the year 589. In 2014, Saint David’s Day falls on a Saturday. Wales is part of the United Kingdom. It is a country with a long and interesting history. Welsh people have their own language (Cymraeg), customs and traditions. Saint David’s Day is an important festival for Welsh people. Saint David’s Day has been an important national day in Wales for many centuries. Leeks and daffodils are Welsh national symbols. On Saint David’s Day, it is traditional for Welsh people to pin a leek or a daffodil to their coasts or jackets. Many girls in Wales dress up in traditional Welsh national costumes on the day. Concerts and parades to celebrate Saint David’s Day are held in Cardiff (the Welsh capital city) and also lots of other towns and cities. The flag of St. David is flown throughout Wales. Many people in Wales go to poetry readings or attend special church services. Câu 1. On which day is Saint David’s Day celebrated? A. May 1st B. March 1st C. March 3rd D. the date changes yearly Câu 2. How long has Saint David’s Day been celebrated as an important national day in Wales? A. for tens of years B. for hundreds of years C. for a hundred year D. for some of years Câu 3. Which city is the capital of Wales? 2 điểm A. London B. Cardiff C. Belfast D. Edinburgh Câu 4. What are the Welsh national symbols? Tùy chọn 1A. the leek and the potato C. the daffodil and the thistle B. the leek and the thistle D. the daffodil and the leek Câu 5. How do people celebrate Saint David’s Day in towns and cities? A. with concerts and parades C. with fireworks displays and parties B. with carnivals and fiestas D. with readings and services