sin21°cos39°+cos21°sin39°=

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°+…+sin288°+sin289°+sin290°= ___ ． 计算：sin21°+sin22°+sin23°+…+sin287°+sin288°+sin289°． 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 sin15°sin75°=? cos36°-cos72°=? 78°18’=( )° sin15°+cos165°= sin15°+sin75°=? sin10°sin30°sin50°sin70°=? sin30°cos60°+cos30°sin60°=