Each year there is an increasing number of cars on roads and streets as millions of new cars and trucks are produced. One out of every six Americans works at putting together the parts of cars, driv
Halloween is round the corner. Kids everywhere are counting down the days. Dentists are refilling their printer inks for all those upcoming bills. And parents are left wondering, “Should I let m
的终边落在直线
上，求
和
的值．
，
或
，
，
，若角
的终边在射线
上，则
，
，
，
．由三角函数的定义知
上，则
，
．由三角函数的定义知