求sin39°-sin21°/cos39°-cos21°的值

1.比大小：tan21°和tan31°；2.sin21°和cos21°；3.cos21°和cos22° 化简：cos21°+cos22°+cos23°+…+cos289°． 计算：sin21°+sin22°+sin23°+…+sin287°+sin288°+sin289°． 计算：sin21°+sin22°+sin23°+…+sin288°+sin289°+sin290°= ___ ． 不求值,分别比较下列各组中两个三角函数值的大小(1)sin21/5π与sin42/5π sin1/5与cos5 求sin15°+cos165°的值 求sin15°×sin75°的值 cos1615°8' 求三角函数的值 cos(-519°)求三角函数的值 tan15°+cos15°/sin15°的值 求详解 求sin15°+tan30°cos15°的值 求cos20°cos40°cos80°的值