| | píng fāng hé gōng shì n(n+1)(2n+1)/6
jí 1^2+2^2+3^2+ … +n^2=n(n+1)(2n+1)/6( zhù: n^2=n de píng fāng )
zhèng míng 1 + 4+ 9+…+ n^2 = n(n+1)(2n+1)/6
zhèng fǎ yī( guī nà cāi xiǎng fǎ):
1、 n= 1 shí, 1= 1( 1+ 1)( 2×1+ 1) /6= 1
2、 n= 2 shí, 1+ 4= 2( 2+ 1)( 2×2+ 1) /6= 5
3、 shè n= x shí, gōng shì chéng lì, jí 1+ 4+ 9+…+ x2= x(x+1)(2x+1)/6
zé dāng n= x+ 1 shí,
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
yě mǎn zú gōng shì
4、 zōng shàng suǒ shù, píng fāng hé gōng shì 1^2+2^2+3^2+… +n^2=n(n+1)(2n+1)/6 chéng lì, dé zhèng。
zhèng fǎ 'èr( lì yòng héng děng shì (n+1)^3=n^3+3n^2+3n+1):
(n+1)^3-n^3=3n^2+3n+1,
n^3-(n-1)^3=3(n-1)^2+3(n-1)+1
..............................
3^3-2^3=3*(2^2)+3*2+1
2^3-1^3=3*(1^2)+3*1+1.
bǎ zhè n gè děng shì liǎng duān fēn bié xiāng jiā, dé:
(n+1)^3-1=3(1^2+2^2+3^2+....+n^2)+3(1+2+3+...+n)+n,
yóu yú 1+2+3+...+n=(n+1)n/2,
dài rén shàng shì dé:
n^3+3n^2+3n=3(1^2+2^2+3^2+....+n^2)+3(n+1)n/2+n
zhěng lǐ hòu dé:
1^2+2^2+3^2+....+n^2=n(n+1)(2n+1)/6 | | zhèng fǎ yī
( guī nà cāi xiǎng fǎ):
1、 N= 1 shí, 1= 1( 1+ 1)( 2×1+ 1) /6= 1
2、 N= 2 shí, 1+ 4= 2( 2+ 1)( 2×2+ 1) /6= 5
3、 shè N= x shí, gōng shì chéng lì, jí 1+ 4+ 9+…+ x2= x(x+1)(2x+1)/6
zé dāng N= x+ 1 shí,
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
yě mǎn zú gōng shì
4、 zōng shàng suǒ shù, píng fāng hé gōng shì 1^2+2^2+3^2+… +n^2=n(n+1)(2n+1)/6 chéng lì, dé zhèng。
zhèng fǎ 'èr
( lì yòng héng děng shì (n+1)^3=n^3+3n^2+3n+1):
(n+1)^3-n^3=3n^2+3n+1,
n^3-(n-1)^3=3(n-1)^2+3(n-1)+1
..............................
3^3-2^3=3*(2^2)+3*2+1
2^3-1^3=3*(1^2)+3*1+1.
bǎ zhè n gè děng shì liǎng duān fēn bié xiāng jiā, dé:
(n+1)^3-1=3(1^2+2^2+3^2+....+n^2)+3(1+2+3+...+n)+n,
yóu yú 1+2+3+...+n=(n+1)n/2,
dài rù shàng shì dé:
n^3+3n^2+3n=3(1^2+2^2+3^2+....+n^2)+3(n+1)n/2+n
zhěng lǐ hòu dé:
1^2+2^2+3^2+....+n^2=n(n+1)(2n+1)/6
a^2+b^2=a(a+b)-b(a-b)
zhèng fǎ sān
( jiàn xià tú):
zhèng fǎ sì
( pái liè zǔ hé fǎ, jiàn xià tú): |
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