1平方+3平方+5平方+7平方+…………+n平方=? 有什么直接的公式 把n代入就可算出 1平方+3平方+5平方……+99平方=?
1\u5e73\u65b9+2\u5e73\u65b9+3\u5e73\u65b9+4\u5e73\u65b9+\u2026\u2026\u2026\u2026+n\u5e73\u65b9=? \u6709\u4ec0\u4e48\u76f4\u63a5\u7684\u516c\u5f0f \u628an\u4ee3\u5165\u5c31\u53ef\u7b97\u51fan(n+1)(2n+1)/6.
\u5bf9(n+1)^3 - n^3 = 3n^2 + 3n + 1\u6c42\u548c:
(n+1)^3 - n^3 = 3n^2 + 3n + 1
n^3 - (n-1)^3 = 3(n-1)^2 + 3(n-1) + 1
\u2026\u2026
2^3 - 1^3 = 3*1^2 + 3*1 + 1
\u76f8\u52a0\u540e\uff1a(n+1)^3 - 1^3 = 3\uff081^2 + \u2026\u2026 + n^2\uff09+ 3\uff081+2+ \u2026\u2026 + n\uff09+\uff081+\u2026\u2026 +1\uff09
\uff1a(n+1)^3 - 1^3 = 3\uff081^2 + \u2026\u2026 + n^2\uff09+ 3\uff08n*(n+1)/2\uff09+n\uff0c\u6574\u7406\u540e\u65e2\u5f97\u3002
an = (2n-1)^2
= 4n^2 -4n +1
= 4n(n-1) +1
= (4/3)[ (n-1)n(n+1) -(n-2)(n-1)n ] + 1
Sn = a1+a2+...+an
=(4/3)(n-1)n(n+1) + n
1^2+2^2+...+99^2
=S50
=(4/3)(49)(50)(51) + 50
=166650
因为(1+a)^3=a^3+3*a^2+3*a+1
所以有
(1+1)^3=1^3+3*1+3*1+1
(1+2)^3=2^3+3*2+3*2+1
(1+3)^3=3^3+3*3+3*3+1
……
(1+n)^3=n^3+3*n+3*4+1
累加,
(1+n)^3=1+3*S+3*(1+2+3+…+n)+n
所以,S= =n*(n+1)*(2n+1)/6
1的平方+2的平方+3的平方+...+n的平方=(n*(n+1)*(2n+1))/6
证明1+4+9+……+N2=N(N+1)(2N+1)/6
1,N=1时,1=1(1+1)(2×1+1)/6=1
2,N=2时,1+4=2(2+1)(2×2+1)/6=5
3,设N=x时,公式成立,即1+4+9+……+x2=x(x+1)(2x+1)/6
则当N=x+1时,
1+4+9+……+x2+(x+1)2=x(x+1)(2x+1)/6+(x+1)2
=(x+1)[2(x2)+x+6(x+1)]/6
=(x+1)[2(x2)+7x+6]/6
=(x+1)(2x+3)(x+2)/6
=(x+1)[(x+1)+1][2(x+1)+1]/6
也满足公式
4,综上所述,平方和公式1+4+9+……+N2=N(N+1)(2N+1)/6成立,得证
绛旓細灏忓1鍒20鐨骞虫柟鏁扮殑鍙h瘈濡備笅 1²=1 2²=4 3²=9 4²=16 5²=25 6²=36 7²=49 8²=64 9²=81 10²=100 11²=121 12²=144 13²=169 14²=196 15²=225 16²=256 17²=289 18&...
绛旓細1鍒25骞虫柟鍙h瘈锛1-9鐨勫钩鏂癸細鍘熸暟鍔犲熬鏁帮紝灏惧钩鏂癸紱閫10杩涗綅锛11-19鐨勫钩鏂癸細灏惧姞15锛10鍑忓熬鍐嶅钩鏂癸紝鍗2浣嶏紱20-25鐨勫钩鏂癸細灏惧姞浜屽崄浜旓紝灏惧钩鏂瑰崰2浣嶃1鍒20鐨勫钩鏂规牴锛1²=1锛2²=4锛3²=9锛4²=16锛5²=25锛6²=36锛7²=49锛8²=64锛9...
绛旓細1² = 1锛 2² = 4 锛3² = 9锛 4² = 16锛 5² = 25锛 6² = 36 锛7² = 49 锛8² = 64 锛9² = 81 锛10² = 100銆11² = 121锛 12² = 144 锛13² = 169 锛14² = 196 锛15²...
绛旓細鍦ㄦ暟瀛 1 鍒 40 涓紝姣忎釜鏁板瓧瀵瑰簲鐨骞虫柟鏁板彲浠ュ憟鐜板嚭涓涓瑙勫緥銆傝寰嬪涓嬶細1 鐨勫钩鏂 = 1锛2 鐨勫钩鏂 = 4锛3 鐨勫钩鏂 = 9锛4 鐨勫钩鏂 = 16锛5 鐨勫钩鏂 = 25锛6 鐨勫钩鏂 = 36锛7 鐨勫钩鏂 = 49锛8 鐨勫钩鏂 = 64锛9 鐨勫钩鏂 = 81锛10 鐨勫钩鏂 = 100 瑙傚療涓婅堪骞虫柟鏁扮殑涓綅鏁帮紝鍙互鐪嬪嚭杩欎簺...
绛旓細鏈涓涓鍏紡锛1²+2²+3²+...+n²=n(n+1)(2n+1)/6 鎵浠1²+2²+...+49²=49*50*99/6=40425 杩樻湁涓涓叕寮1^3+2^3+...+n^3=[n(n+1)/2]^2
绛旓細濂囨暟鐨骞虫柟=(2n-1)²锛宯=1锛2锛3鈥︹﹀伓鏁扮殑骞虫柟=(2n)²锛宯=1锛2锛3鈥︹﹀鏁扮殑绔嬫柟=(2n-1)³锛宯=1锛2锛3鈥︹﹀伓鏁扮殑绔嬫柟=(2n)³锛宯=1锛2锛3鈥︹﹁灏忓鐢熷氨鍋氳繖涓湡娌¢亾寰
绛旓細瑙g瓟锛氬湪绾挎暟瀛﹀府鍔╀綘锛侊紒锛佽繖鏄涓涓璁$畻骞虫柟鍏紡锛1^2+2^2+3^2+...+n^2=n(n+1)(2n+1)/6 鍥犳鏈夛細n=10 閭d箞锛10X锛10+1锛夛紙20+1锛/6=385锛涗絾鎰垮浣犳湁甯姪锛侊紒锛佺浣犲涔犳剦蹇紒锛
绛旓細9#178=81锛10#178=100锛11#178=121锛12#178=144锛13#178=銆1骞虫柟鏄2锛2骞虫柟鏄4锛3骞虫柟鏄9锛4骞虫柟鏄16锛5骞虫柟鏄25锛6骞虫柟鏄36锛7骞虫柟鏄49锛8骞虫柟鏄64锛9骞虫柟鏄81锛10骞虫柟鏄100锛11骞虫柟鏄121锛12骞虫柟鏄144锛13骞虫柟鏄169锛14骞虫柟鏄196锛15骞虫柟鏄225锛16骞虫柟鏄256锛17骞虫柟鏄289锛18骞虫柟鏄...
绛旓細1²锛3²锛5²锛7²...+51²=(2脳1-1)^2+(2脳2-1)^2+...(2脳26-1)^2 =4(1^2+2^2+...+26^2)-4(1+2+...+26)+51 =4脳(26)(26+1)(53)/6-4脳26脳(1+26)/2+51 =24804-1404+51 =23451 ...
绛旓細5²=(2脳3-1)²=4脳3²-4脳3+1.7²=(2脳4-1)²=4脳4²-4脳4+1 锛岋紝锛47²=(2脳24-1)²=4脳24²-4脳24+1 49²=(2脳25-1)²=4脳25²-4脳25+1.绱姞鍙煡锛屽師寮=4(1²+2²+3²+4&...