sina＞0,cosb＞0,sinc＞0log(2) sina-log(2)cosb-loog(2)sinc=1 即 sina/(cosbsinc)=2sina=2cosbsinccosb= sina/（2sinc)a/sina=c/sinc即 cosb= a/(2c)=(a²+c²-b²)/2acc（a²+c²-b²)=a...