帮个忙,帮我出50道人教版初三物理密度填空题!十万火急
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帮个忙,帮我出50道人教版初三物理密度填空题!十万火急
一定填空题哦
一定填空题哦
![帮个忙,帮我出50道人教版初三物理密度填空题!十万火急](/uploads/image/z/1428718-22-8.jpg?t=%E5%B8%AE%E4%B8%AA%E5%BF%99%2C%E5%B8%AE%E6%88%91%E5%87%BA50%E9%81%93%E4%BA%BA%E6%95%99%E7%89%88%E5%88%9D%E4%B8%89%E7%89%A9%E7%90%86%E5%AF%86%E5%BA%A6%E5%A1%AB%E7%A9%BA%E9%A2%98%21%E5%8D%81%E4%B8%87%E7%81%AB%E6%80%A5)
an是方程(n^2+n)x^2+(n^2+n-1)x-1=0的根 ,解得 an=1/(n^2+n) 或an=-1(舍)
即an=1/[n*(n+1)] =1/n-1/(n+1)
Sn=a1+a2+a3+.+an
=1-1/2+1/2-1/3+1/3-.+1/n-1/(n+1)
=1-1/(n+1)
=n/(n+1)
limSn=1
即an=1/[n*(n+1)] =1/n-1/(n+1)
Sn=a1+a2+a3+.+an
=1-1/2+1/2-1/3+1/3-.+1/n-1/(n+1)
=1-1/(n+1)
=n/(n+1)
limSn=1