三角函数化简三角函数化简(cot
省略“度”：
cos15cos25cos35cos85
=(1/4)[(cos40+cos10)(cos120+cos50)]
=(1/4)[(cos40+cos10)(cos50-1/2)]
=(1/8)[2cos50cos40+2cos50cos10-cos40-cos10]
=(1/8)[cos90+cos10+cos60+cos40-cos40-cos10]
=(1/16)
sin15sin25sin35sin85
=(1/4)[(cos40-cos10)(cos120-cos50)]
=-(1/4)[(cos40-cos10)(cos50+1/2)]
=-(1/8)[2cos50...全部
省略“度”：
cos15cos25cos35cos85
=(1/4)[(cos40+cos10)(cos120+cos50)]
=(1/4)[(cos40+cos10)(cos50-1/2)]
=(1/8)[2cos50cos40+2cos50cos10-cos40-cos10]
=(1/8)[cos90+cos10+cos60+cos40-cos40-cos10]
=(1/16)
sin15sin25sin35sin85
=(1/4)[(cos40-cos10)(cos120-cos50)]
=-(1/4)[(cos40-cos10)(cos50+1/2)]
=-(1/8)[2cos50cos40-2cos50cos10+cos40-cos10]
=-(1/8)[cos90+cos10-cos60-cos40+cos40-cos10]
=(1/16)
--->cot15cot25cot35cot85
=cos15cos25cos35cos85/(sin15sin25sin35sin85)
=1
。
收起
