常用傅里叶级数展开式怎么证明 高等数学,傅里叶级数,展开式多加了a0/2,f(x)不用减去...
\u5085\u91cc\u53f6\u7ea7\u6570\u5c55\u5f00\u5f0f\u4ee52l\u4e3a\u5468\u671f\uff0c\u8fd9\u4e2a2l\u5fc5\u987b\u662f\u6700\u5c0f\u5468\u671f\u5417\u697c\u4e3b\u6709\u6ca1\u6709\u6ce8\u610f\u5230
\u7b54\u6848\u4e2dan=(2/\u03c0)\u222bf(x)cosnx dx\uff08\u4ece0\u5230\u03c0\uff09=(1/\u03c0)\u222bf(x)cosnx dx\uff08\u4ece-\u03c0\u5230\u03c0\uff09
\u8fd9\u4e2a\u516c\u5f0f\u662f\u6309\u71672\u03c0\u4e3a\u5468\u671f\u8ba1\u7b97\u7684
\u800c\u697c\u4e3b\u81ea\u5df1\u7684
an=(2/\u03c0)f(x)cos2nxdx\u5728-\u03c0/2\u2192\u03c0/2\u4e0a\u7684\u79ef\u5206
\u662f\u6309\u7167\u03c0\u4e3a\u5468\u671f\u8ba1\u7b97\u7684\uff0c\u4e14an\u5e94\u8be5\u662f(1/\u03c0)\u4e0d\u662f(2/\u03c0)
\u8fd9\u4e2a\u9898\u63092\u03c0\u4e3a\u5468\u671f\u6216\u8005\u03c0\u4e3a\u5468\u671f\u5c55\u5f00\u90fd\u662f\u53ef\u4ee5\u7684\uff0c\u6240\u4ee5\u4f1a\u51fa\u73b0\u8fd9\u6837\u7684\u95ee\u9898\uff0c\u5e94\u8be5\u90fd\u662f\u5bf9\u7684
a0\u4e0d\u662f0\uff0c\u9898\u4e2d\u7684a0\uff1d\u03c0\u5e73\u65b9/3
\u9898\u4e2d\u7684a0\u548c\u516c\u5f0f\u91cc\u7684a0\u4e0d\u4e00\u6837
\u8fd9\u91cc\u505a\u4e86\u6362\u5143\uff0c\u4ee4a0\uff1d\u516c\u5f0f\u91cc\u9762\u7684a0/2
\u7531\u4e8e\uff0c\u5076\u51fd\u6570\u7684\u5085\u7acb\u53f6\u7ea7\u6570\u5c55\u5f00\u5f0f\u4e2dbn\uff1d0
\u8fd9\u6837\u53ef\u4ee5\u5c06a0\u548can\u5408\u5e76\u5728\u4e00\u8d77
\u7d2f\u52a0\u7b26\u53f7\u7684n\u662f\u4ece0\u5230\u65e0\u7a77\u5927
\u8fd9\u9898\u91cc\u9762\uff0cn\uff1d0\u65f6\uff0ca0\u4e0d\u662f\u5085\u7acb\u53f6\u7ea7\u6570\u5c55\u5f00\u5f0f\u7684\u7cfb\u6570
n>0\u65f6\uff0can\u662f\u5085\u7acb\u53f6\u7ea7\u6570\u5c55\u5f00\u5f0f\u7684\u7cfb\u6570
a0/2\u7684\u90a3\u4e2a\u516c\u5f0f
\u662f\u5bf9\u4efb\u610f\u7684\u5468\u671f\uff1d2\u03c0\u7684f(x)
a0\u63d0\u51fa\u6765\uff0can\u548cbn\u5408\u5e76\u5728\u4e00\u8d77
\u7d2f\u52a0\u7b26\u53f7\u7684n\u662f\u4ece1\u5230\u65e0\u7a77\u5927
\u8fc7\u7a0b\u5982\u4e0b\uff1a
绛旓細璇佹槑锛氭牴鎹鍌呴噷鍙剁骇鏁鐨勫畾涔夛紝鑻ュ皢f(x)灞曞紑鎴愪綑寮︾骇鏁帮紝鍒檉(x)=(a0)/2+鈭慳ncosnx锛屽叾涓紝an=(2/蟺)鈭(0,蟺)f(x)cosnxdx锛宯=0,1,2锛屸︼紝鈭炪傛湰棰樹腑锛宖(x)=sinx锛屽垯an=(2/蟺)鈭(0,蟺)sinxcosnxdx銆 鈭碼0=(2/蟺)鈭(0,蟺)sinxdx=(-2/蟺)cosx涓(x=0,蟺)=4/蟺锛宎1=鈭...
绛旓細绗竴姝ワ細璁$畻鍌呴噷鍙剁郴鏁 鏍规嵁鍛ㄦ湡鍑芥暟鐨勫畾绉垎鎬ц川锛岀敱浠ヤ笅鍏紡璁$畻鍑芥暟f(x)鍦ㄤ换鎰忓尯闂撮暱搴︿负2蟺鐨勫尯闂翠笂鐨勫畾绉垎.涓鑸彇涓虹洿鎺ュ畾涔夊嚱鏁扮殑涓涓懆鏈熷尯闂淬傚父鍙栦负[-蟺, 蟺]锛屽嵆 绗簩姝ワ細浠ュ倕閲屽彾绯绘暟涓虹郴鏁帮紝鍐欏嚭涓夎绾ф暟 绗笁姝ワ細鍩轰簬鐙勫埄鍏嬮浄鏀舵暃瀹氱悊鍒ゅ畾鍌呴噷鍙剁骇鏁鐨勬敹鏁涙 鐙勫埄鍏嬮浄鏀舵暃瀹氱悊锛...
绛旓細bn=(1/蟺)鈭(-蟺,蟺)f(x)sinnxdx=(2/蟺)鈭(0,蟺)sinnxdx=-[2/(n蟺)]cosnx涓(x=0,蟺)=-[(-1)^n-1]/(n蟺)銆傗埓n涓哄伓鏁版椂锛宐n=0銆乶涓哄鏁版椂锛宐n=4/(n蟺)銆
绛旓細瀵逛簬鎴戜滑鐔熸倝鐨勫厜婊戝嚱鏁帮紝鍌呴噷鍙剁骇鏁纭疄鍙互绋冲畾鍦灞曞紑锛岃繖涓烘垜浠彁渚涗簡寮哄ぇ鐨勫垎鏋愬伐鍏枫傚敖绠¤缁嗙殑璇佹槑杩囩▼绻佺悙锛屼絾瀵逛簬鏁板鐖卞ソ鑰呮潵璇达紝鍙傝冧功绫嶅[2]鍜孾3]鏄粷浣崇殑寮曞銆傚鏋滀綘娌℃湁澶鏃堕棿锛屽揩閫熸祻瑙堟暟瀛﹀垎鏋愭暀鏉愪腑鐨勭浉鍏崇珷鑺傦紝涔熻冻浠ラ鐣ュ叾绮鹃珦鈥斺旀瘯绔燂紝杩欎簺鐭ヨ瘑瀵瑰疄闄呭簲鐢ㄨ嚦鍏抽噸瑕併
绛旓細鍌呴噷鍙剁骇鏁板睍寮鍏紡濡備笅锛氬倕閲屽彾绾ф暟鍍忎笁瑙掓尝锛岀煩褰㈡尝锛屾褰㈡尝杩欑娉㈠舰涓嶈繛缁紝鍥犳鍦ㄤ豢鐪熻蒋浠朵腑寰堝鏄撳嚭鐜拌绠椾笉鏀舵暃鐨勬儏鍐点傛墍浠ワ紝鍦ㄨ繖绉嶆儏鍐典笅锛屽埄鐢ㄤ竴绯诲垪璋愭尝鍙犲姞鐨勫舰寮忔潵绛変环浜庡師鏉ョ殑娉㈠舰锛屽彲浠ュ緢濂界殑浼樺寲妯″瀷銆傚倕閲屽彾灞曞紑寮忔敹鏁涙у垽鍒 鑷充粖杩樻病鏈夊垽鏂倕閲屽彾绾ф暟鐨勬敹鏁涙у厖鍒嗗繀瑕佹潯浠讹紝浣嗘槸瀵逛簬瀹為檯...
绛旓細鎶婇潪姝e鸡鍛ㄦ湡鍑芥暟f(t)灞曞紑鎴愬倕閲屽彾绾ф暟涔熺О涓鸿皭娉㈠垎鏋愩傚伐绋嬪疄闄呬腑鎵閬囧埌鐨勯潪姝e鸡鍛ㄦ湡鍑芥暟澶х害鏈夊崄浣欑锛屽畠浠殑鍌呴噷鍙剁骇鏁板睍寮寮鍓嶄汉閮藉凡浣滃嚭锛屽彲浠庡悇绉嶆暟瀛︿功绫嶄腑鐩存帴鏌ョ敤銆備粠寮忥紙10-2-3锛変腑鐪嬪嚭锛屽皢n鎹㈡垚(-n)鍚庡嵆鍙璇佹槑鏈 a-n=an b-n=-bn A-n=An 蠄-n=-蠄n 鍗砤n鍜孉n鏄鏁e彉閲弉...
绛旓細x)锛屽彲浠ョ敤涓夎鍑芥暟鐨勭骇鏁板睍寮琛ㄧず锛氬叾涓璦n鍜宐n鏄郴鏁帮紝鍙互閫氳繃鍑芥暟)f(x)姹傚緱銆傝繖绉嶅睍寮鏂瑰紡绉颁负涓夎绾ф暟灞曞紑銆傛垜浠繕鍙互灏嗕笁瑙掑嚱鏁板啓鎴愬鎸囨暟褰㈠紡锛氬皢鍏朵唬鍏ヤ笂寮忓緱鍒帮細鍏朵腑锛歝n灏辨槸f(x)鐨勫倕閲屽彾绯绘暟锛屽弽杩囨潵锛鍌呴噷鍙剁骇鏁板睍寮寮鍙互鍐欎负锛氳繖鏍凤紝鎴戜滑灏卞緱鍒颁簡鍌呴噷鍙跺彉鎹
绛旓細棣栧厛锛屾垜浠渶瑕佽绠楀嚭c_n鐨勫硷紝鍙互浣跨敤浠ヤ笅鍏紡锛歝_n = (2/蟺) * 鈭玙{-1}^{1} f(x) * T_n(x) * dx 瀵逛簬f(x) = x^2锛屾垜浠彲浠ュ皢瀹灞曞紑鎴愬箍涔鍌呴噷鍙剁骇鏁锛歠(x) = 鈭慱{n=-鈭瀩^{鈭瀩 c_n T_n(x)f(x) = 鈭慱{n=-鈭瀩^{鈭瀩 (2/蟺) * 鈭玙{-1}^{1} x^2 ...
绛旓細鍌呴噷鍙剁骇鏁板睍寮鍏紡鏄 F^(蠅)=鈭紙涓婇檺+鈭,涓嬮檺-鈭)f(t)exp(-i蠅t)dt銆傚倕閲屽彾灞曞紑寮忔槸鎸囩敤涓夎绾ф暟琛ㄧず鐨勫舰寮忥紝鍗充竴涓嚱鏁扮殑鍌呴噷鍙剁骇鏁板湪瀹冩敹鏁涗簬姝ゅ嚱鏁版湰韬椂鐨勪竴绉嶇О鍛笺傝嫢鍑芥暟f(x)鐨勫倕閲屽彾绾ф暟澶勫鏀舵暃浜巉 (x)锛屽垯姝ょ骇鏁扮О涓篺(x)鐨勫倕閲屽彾灞曞紑寮忋傛ц川 1銆佹敹鏁涙 鍌呴噷鍙剁骇鏁扮殑...
绛旓細鍌呴噷鍙灞曞紑寮鏄寚鐢ㄤ笁瑙掔骇鏁拌〃绀虹殑褰㈠紡锛屽嵆涓涓嚱鏁扮殑鍌呴噷鍙剁骇鏁鍦ㄥ畠鏀舵暃浜庢鍑芥暟鏈韩鏃剁殑涓绉嶇О鍛笺傝嫢鍑芥暟f(x)鐨勫倕閲屽彾绾ф暟澶勫鏀舵暃浜巉(x)锛屽垯姝ょ骇鏁扮О涓篺(x)鐨勫倕閲屽彾灞曞紑寮忋傚湪宸ョ▼搴旂敤涓紝涓鑸亣瀹氬倕閲屽彾绾ф暟闄や簡鍦ㄤ笉杩炵画鐐逛互澶栧澶勬敹鏁涳紝鍘熷洜鏄伐绋嬩笂閬囧埌鐨勫嚱鏁版瘮鏁板瀹舵彁渚涚殑杩欎釜鍋囧畾鐨勫弽渚...