0.9+0.99+0.999+0.9999+.0.99...9(有N个9)=?
问题描述:
0.9+0.99+0.999+0.9999+.0.99...9(有N个9)=?
答
=1-0.1+1-0.01+1-0.001+...+1-0.000...00(N个0)1
=N-0.1111...111(N个1)
答
=1-0.1+1-0.01+1-0.001+...=n-0.111111111(n个)