f1?n??f2?n??f3?n??sinn??au?n??[??n??a??n?1?]n这里用到性质： u?n????n??u?n?1?
an??n??a0??n????n?
?sinn???anu?n????n??anu?n??a??n?1???sinn???anu?n??an?1u?n????n?1???sinn???anu?n??an?1u?n????n?1?? ?sinn???anu?n??anu?n?1???sinn???an[??n??u?n?1?]?anu?n?1???sinn????n??sinn?16