cosa=13/20+(5/12)sina,①∴1=sin^a+[13/20+(5/12)sina]^=(169/144)sin^a+(13/24)sina+169/400,(169/144)sin^a+(13/24)sina-231/400=0,繁!△=169/576+169*231/14400=169*256/14400=169*4/225,sina=[-13/24土26/15]/(...