1/1x4+1/4x7+1/7x10+...+1/73x76=? 急啊······

来源:学生作业帮助网 编辑:作业帮 时间:2024/12/02 11:06:53
1/1x4+1/4x7+1/7x10+...+1/73x76=? 急啊······
xPN@]l)t:qQ& PƘ`$р.$A&.P7 #D~K_8-Y&f{Μ1FU%TWbYZn5`15'rr%FpkBJR%4MJQ1׎FD02)q~a]b56(Tr e=nUke7EnT#%Q".KvqlEfCYDkkLxFtjP

1/1x4+1/4x7+1/7x10+...+1/73x76=? 急啊······
1/1x4+1/4x7+1/7x10+...+1/73x76=? 急啊······

1/1x4+1/4x7+1/7x10+...+1/73x76=? 急啊······
1/1x4+1/4x7+1/7x10+...+1/73x76
=1/3(1-1/4+1/4-1/7+...+1/73-1/76)
=1/3*75/76
=25/76

1/a*(a+3)然后a从1到73
 double d=0.0;
 for(int i=1;i<=73;i+=3){
 d+=new Double(1.0)/new Double(i)*new Double((i+3));
 System.out.println(d);
 }
 System.out.println(d);

答案是31.344288162105848

证明很简单.. 若x是实数,不是整数,设x的小数部分为k,整数部分x-k=m, 则左侧为[(m-1) k][(m-2) k][(m-3) k][(m-4) k]=整数 k*