求连续几个奇数的平方和
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求连续几个奇数的平方和
1的平方+2的平方+3的平方+-------+n的平方=?
1的平方+2的平方+3的平方+-------+n的平方=?
=1²+2²+3²+.+n²
=n(n+1)(2n+1)/6
由于1²+2²+3²+.+(2n)²
=2n(2n+1)(4n+1)/6
=n(2n+1)(4n+1)/3
所以n(2n+1)(4n+1)/3=S+2n(n+1)(2n+1)/3
S=n(2n+1)(4n+1)/3-2n(n+1)(2n+1)/3
=n[(2n+1)(4n+1)-2(n+1)(2n+1)]/3
=n[(2n+1)(4n+1-2n-2)]/3
=n[(2n+1)(2n-1)]/3
=n(4n²-1)/3
懂了吗
=n(n+1)(2n+1)/6
由于1²+2²+3²+.+(2n)²
=2n(2n+1)(4n+1)/6
=n(2n+1)(4n+1)/3
所以n(2n+1)(4n+1)/3=S+2n(n+1)(2n+1)/3
S=n(2n+1)(4n+1)/3-2n(n+1)(2n+1)/3
=n[(2n+1)(4n+1)-2(n+1)(2n+1)]/3
=n[(2n+1)(4n+1-2n-2)]/3
=n[(2n+1)(2n-1)]/3
=n(4n²-1)/3
懂了吗