2²-4²+6²-8²+...-48²+50²
1个回答
展开全部
an
=n^2
=n(n+1) -n
=(1/尘梁薯3)[n(n+1)(n+2)-(n-1)n(n+1)] -(1/2)[n(n+1)-(n-1)n]
Sn
=a1+a2+...+an
=(1/3)n(n+1)(n+2) -(1/派者2)n(n+1)
=(1/6)n(n+1)[2(n+2) -3]
=(1/渣贺6)n(n+1)(2n+1)
2^2-4^2+6^2-8^2+...-48^2+50^2
=4x(1^2-2^2+3^2-4^2+...-24^2+25^2)
=4x(1^2+2^2+...+25^2)-8x(2^2+4^2+...+24^2)
=4x(1^2+2^2+...+25^2)-32x(1^2+2^2+...+12^2)
=4S25-32S12
=(2/3)(25)(26)(51) - (16/3)(12)(13)(25)
=1300
=n^2
=n(n+1) -n
=(1/尘梁薯3)[n(n+1)(n+2)-(n-1)n(n+1)] -(1/2)[n(n+1)-(n-1)n]
Sn
=a1+a2+...+an
=(1/3)n(n+1)(n+2) -(1/派者2)n(n+1)
=(1/6)n(n+1)[2(n+2) -3]
=(1/渣贺6)n(n+1)(2n+1)
2^2-4^2+6^2-8^2+...-48^2+50^2
=4x(1^2-2^2+3^2-4^2+...-24^2+25^2)
=4x(1^2+2^2+...+25^2)-8x(2^2+4^2+...+24^2)
=4x(1^2+2^2+...+25^2)-32x(1^2+2^2+...+12^2)
=4S25-32S12
=(2/3)(25)(26)(51) - (16/3)(12)(13)(25)
=1300
已赞过
已踩过<
评论
收起
你对这个回答的评价是？
推荐律师服务：
若未解决您的问题，请您详细描述您的问题，通过百度律临进行免费专业咨询
