Huhuhu,các bạn giải nhanh giúp mik nha,mik đang cần rất gấp đó ! T^T

Dễ lắm:)

Ta có: \(\frac{1}{176}+\frac{1}{336}+\frac{1}{546}+...+\frac{1}{3416}+\frac{1}{4026}\)

\(=\frac{1}{11.16}+\frac{1}{16.21}+\frac{1}{21.26}+...+\frac{1}{56.61}+\frac{1}{61.66}\)

\(=\frac{1}{5}\cdot\left(\frac{5}{11.16}+\frac{5}{16.21}+\frac{5}{21.26}+...+\frac{5}{56.61}+\frac{5}{61.66}\right)\)

\(=\frac{1}{5}\cdot\left(\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+\frac{1}{21}-\frac{1}{26}+...+\frac{1}{56}-\frac{1}{61}+\frac{1}{61}-\frac{1}{66}\right)\)

\(=\frac{1}{5}\cdot\left(\frac{1}{11}-\frac{1}{66}\right)\)

\(=\frac{1}{5}\cdot\frac{5}{66}=\frac{1}{66}\)

Uk,tớ tìm ra ĐA rồi,cậu lm đúng ồi,nhưng tớ lm kiểu khác cơ.

Hộ mi với ai nhanh mi k nha

\(D=\frac{1}{6}+\frac{1}{66}+\frac{1}{176}+\frac{1}{336}+\frac{1}{546}\)

\(D=\frac{1}{1.6}+\frac{1}{6.11}+\frac{1}{11.16}+\frac{1}{16.21}+\frac{1}{21.26}\)

\(D=\frac{1}{5}\left(\frac{5}{1.6}+\frac{5}{6.11}+\frac{5}{11.16}+\frac{5}{16.21}+\frac{5}{21.26}\right)\)

\(D=\frac{1}{5}\left(\frac{1}{1}-\frac{1}{6}+\frac{1}{6}-\frac{1}{11}+...+\frac{1}{21}-\frac{1}{26}\right)\)

\(D=\frac{1}{5}\left(\frac{1}{1}-\frac{1}{26}\right)\)

\(D=\frac{1}{5}.\frac{25}{26}=\frac{5}{26}\)

\(x+\frac{5}{3}=\frac{1}{81}\)

\(x=\frac{1}{81}-\frac{5}{3}\)

\(x=\frac{-134}{81}\)

\(x+\frac{5}{3}=\frac{1}{81}\)

\(\Leftrightarrow x=\frac{1}{81}-\frac{5}{3}\)

\(\Leftrightarrow x=-\frac{134}{81}\)

\(-52+\frac{2}{3}x=-46\)

\(\Leftrightarrow\frac{2}{3}x=-46+52\)

\(\Leftrightarrow\frac{2}{3}x=6\)

<=> 2x = 6.3

<=> 2x = 18

=> x = 9

\(\frac{x}{45}=\frac{5}{6}+\frac{-29}{30}\)

(có thể hơi khó hiểu từ bước 2, bạn lấy mẫu số chung là 30 nhé)

\(\Leftrightarrow\frac{x}{45}=\frac{25}{30}-\frac{29}{30}\)

\(\Leftrightarrow\frac{x}{45}=\frac{25-29}{30}\)

\(\Leftrightarrow\frac{x}{45}=\frac{-4}{30}\)

\(\Leftrightarrow\frac{x}{45}=\frac{-2}{15}\)

\(\Leftrightarrow x=45\left(-\frac{2}{15}\right)\)

=> x = -6

1/6+1/66+1/176+....+1/496.501

=1/1.6+1/6.11+1/11.16+....+1/496.501

=(1/5).(5/1.6+5/6.11+5/11.16+....+5/496.501)

=(1/5).(1-1/6+1/6-1/11+1/11-1/16+...+1/496-1/501)

=(1/5).(1-1/501)

=1/5 . 500/501

=100/501

Ta có: 1/6+1/66+1/176+1/336+...+1/496.501

         =1/1.6+1/6.11+1/11.16+1/16.21+...+1/496.501

         =1/5.(5/1.6+5/6.11+5/11.16+5/16.21+...+5/496.501)

         =1/5.(1-1/6+1/6-1/11+1/11-1/16+1/16-1/21+...+1/496-1/501)

         =1/5.(1-1/501)

         =1/5.500/501

         =100/501

đúng không trần hương giang

6+66+176+336+546=1130

B= 1/1*6+1/6*11+1/11*16+1/16*21+.....+1/496+501

Nhan B voi 5 ta duoc

B*5=5/1*6   +  5/6*11+  5/11*16  +5/16*21+....+5/496+501

B*5=1/1-1/6+1/6-1/11+1/11-1/16 +1/16-1/21+...+1/496-1/501

B*5=1-1/501

B*5=500/501

B=500/501: 5=100/501