如图,游客从某旅游景区的景点A处下山至C处有两种路径.一种是从A...
(1)∵cosA=12 13 ,cosC=3 5 ,∴sinA=1?cos2A =5 13 ,sinC=1?cos2C =4 5 可得sinB=sin(A+C)=sinAcosC+cos