5π/8是第二象限角,正弦值 为正,余弦和正切值为负。5π/8<3π/4,正切的绝对值大于1,余弦的绝对值小于1,而二者都为负,所以余弦值大于正切值,所以sin5π/8>cos5π/8>tan5π/8.
解:5π/8是第二象限角所以sin5π/8>0 cos5π/8<0 tan5π/8<0cos5π/8=-sinπ/8>-1 tan5π/8=-cotπ/8= -1/tanπ/8> -1/tan0=-∝所以sin5π/8>cos5π/8>tan5π/8
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