sinA/a=sinB/b=sina/5=sinb/4
sina=5sinb/4
cosa=√(1-25sinb²/16)
cos(a-b)=cosacosb+sinasinb=5sinb²/4+√(1-sinb²)√(1-25sinb²/16)
=31/32
sinb²=t
31/32-5t/4=√(1-t)√(1-25t/16)
961/1024+25t²/16-155t/512=1+25t²/16-41t/25
63/1024=(41x512-155x25)/10240
t=630/7117
饿.好变态.