想问一下，cos4分之9π的值怎么求要过程，和解答谢谢 cos4分之5派求解答过程
cos\uff08-4\u5206\u4e4b23\u03c0\uff09\uff0c\u548csin\uff08-9\u5206\u4e4b34\u03c0\uff09\u7b2c\u51e0\u8c61\u9650\u600e\u4e48\u5224\u65ad\uff0c\u5927\u6148\u5927\u60b2\u6559\u6559\u6211\u5427\u8fd9\u4f4d\u540c\u5b66\uff0c\u6211\u4f30\u8ba1\u4f60\u60f3\u95ee\u7684\u662fcos\uff08-4\u5206\u4e4b23\u03c0\uff09\u548csin\uff08-9\u5206\u4e4b34\u03c0\uff09\u662f\u6b63\u503c\u8fd8\u662f\u8d1f\u503c\u5427\uff1f
\u9996\u5148\u5206\u6790-4\u5206\u4e4b23\u03c0\uff0c\u5148\u628a\u5b83\u6539\u6210-6\u03c0+4\u5206\u4e4b1\u03c0\uff0c\u518d\u628a\u8fd9\u4e2a\u89d2\u5ea6\u53bb\u63892\u03c0\u7684\u6574\u6570\u500d\uff0c\u4f7f\u5269\u4e0b\u7684\u89d2\u5ea6\u521a\u597d\u57280\u52302\u03c0\u4e4b\u95f4\uff0c\u8fd9\u6837\uff0c\u521a\u624d\u7684\u89d2\u5ea6\u5c31\u53d8\u6210\u4e86\u56db\u5206\u4e4b\u4e00\u03c0\uff0c\u800c\u4f59\u7384\u5728\u56db\u4e2a\u8c61\u9650\u7684\u6b63\u8d1f\u60c5\u51b5\u5206\u522b\u4e3a\u6b63\u8d1f\u8d1f\u6b63\uff0c\u7b2c\u4e00\u4e2a\u5f0f\u5b50\u4e3a\u6b63\u503c\u3002\u5982\u679c\u4f60\u8bb0\u4e0d\u4f4f\u4f59\u7384\u5728\u56db\u4e2a\u8c61\u9650\u7684\u6b63\u8d1f\u60c5\u51b5\uff0c\u90a3\u4f60\u5c31\u8bb0\u4f4f\u4f59\u7384\u51fd\u6570\u7684\u56fe\u50cf\uff0c\u4ece\u56fe\u50cf\u4e0a\u5c31\u80fd\u8bb0\u4f4f\u4e86\u3002
\u7b2c\u4e8c\u4e2a\u5f0f\u5b50\u7684\u5224\u65ad\u65b9\u5f0f\u540c\u4e0a\uff0c\u81ea\u5df1\u63a8\u5427\uff01
-\u221a2/2
\u4f7f\u7528\u8bf1\u5bfc\u516c\u5f0f\u5373\u53ef\uff0c\u5982\u4e0bcos\uff085\u03c0/4\uff09=cos\uff08\u03c0+\u03c0/4\uff09=-cos\uff08\u03c0/4\uff09=-\u221a2/2
用诱导公式：
绛旓細鐢ㄨ瀵煎叕寮忥細
绛旓細鎰垮浣犳湁甯姪
绛旓細cos9蟺/4=cos蟺/4=1/2 tan-11蟺/6=tan蟺/6=鏍瑰彿3/3
绛旓細椤轰究璇涓涓嬶紝cos (9/4)蟺=cos(1/4)蟺=鈭(2)/2 tan 蟺/4=1 甯屾湜鎴戠殑鍥炵瓟瀵规偍鏈夊府鍔┿
绛旓細閭ｄ箞COS娲剧殑鍊兼槸浜屽嶇殑鏍瑰彿浜屽悧锛焎os蟺=-1锛宻in蟺=0锛宼an蟺=0锛宑os蟺/4=鈭2/2锛宑os蟺=cos锛4x蟺/4锛夆墵4cos锛埾/4锛夎繖閲屼笉鑳芥彁鍑4鐨勩cos鍥涘垎涔嬩節娲炬槸绛変簬cos(9蟺/4)=cos(2蟺+蟺/4)=cos(蟺/4)=鈭2/2(鐩稿綋浜庤浆浜嗕竴涓2蟺鐨勫懆鏈)銆
绛旓細cos9蟺/4=cos锛2蟺+蟺/4锛=cos蟺/4=鏍瑰彿2/2 sin780掳=sin锛720掳+60掳锛=sin60掳=鏍瑰彿3/2 tan(-7蟺/6锛=tan锛-2蟺+5蟺/6锛=tan锛埾-蟺/6锛=-tan蟺/6=-鏍瑰彿3/3
绛旓細闄や簡杩欎釜娌℃墦娓呮锛-31蟺/4锛夌瓑浜2鍒嗕箣鏍2浠ュ強sin锛-4蟺/3锛夌瓑浜2鍒嗕箣鏍瑰彿3,鍏朵粬閮芥槸瀵圭殑.
绛旓細閭ｄ箞COS娲剧殑鍊兼槸浜屽嶇殑鏍瑰彿浜屽悧锛焎os蟺=-1锛宻in蟺=0锛宼an蟺=0锛宑os蟺/4=鈭2/2锛宑os蟺=cos锛4x蟺/4锛夆墵4cos锛埾/4锛夎繖閲屼笉鑳芥彁鍑4鐨勩cos鍥涘垎涔嬩節娲炬槸绛変簬cos(9蟺/4)=cos(2蟺+蟺/4)=cos(蟺/4)=鈭2/2(鐩稿綋浜庤浆浜嗕竴涓2蟺鐨勫懆鏈)銆
绛旓細鎴鎯抽棶涓涓嬶紝寮忓瓙涓殑鈥渪"鏄粈涔堬紵涓嶇煡鏄笉鏄浣欑殑锛熷鏋滄病鏈墄锛屽簲璇ヨ繖鏍风畻锛(cos蟺/9)(cos2蟺/9)(cos3蟺/9)(cos4蟺/9)=(sin蟺/9)(cos蟺/9)(cos2蟺/9)(cos蟺/3)(cos4蟺/9)/(sin蟺/9)=(sin2蟺/9)(cos2蟺/9)(cos4蟺/9)/[4(sin蟺/9)]=(sin4蟺/9)(cos4蟺/9)...
绛旓細cos锛蟺/4锛夆増0.707銆傁/4鍗充负锛180梅4=45搴︺俢os锛埾/4锛=cos45搴=鈭2/2鈮0.707銆
