Đặt A = 1/5x10 + 1/10x15 + 1/15x20 + 1/20x25 + ... + 1/95x100
A x 5 = 5/5x10 + 5/10x15 + 5/15x20 + 5/20x25 + ... + 5/95x100
A x 5 = 1/5 - 1/10 + 1/10 - 1/15 + 1/15 - 1/20 + 1/20 - 1/25 + ... + 1/95 - 1/100
A x 5 = 1/5 - 1/100
A x 5 = 19/100
A = 19/100 : 5
A = 19/100 x 1/5
A = 19/500
Vậy A= 19/500
chỉ cần phân k nha bạn
kết bạn vs mình nói cho
=\(\frac{1}{5}x\left(\frac{1}{5}-\frac{1}{10}+\frac{1}{10}-\frac{1}{15}+\frac{1}{15}-\frac{1}{20}+...+\frac{1}{95}-\frac{1}{100}\right)\)
=\(\frac{1}{5}x\left(\frac{1}{5}-\frac{1}{100}\right)=\frac{1}{5}x\frac{19}{100}=\frac{19}{500}\)
\(\frac{1}{5.10}+\frac{1}{10.15}+\frac{1}{15.20}+\frac{1}{20.25}+...+\frac{1}{95.100}\)
\(=\frac{1}{5}.\left(\frac{5}{5.10}+\frac{5}{10.15}+\frac{5}{15.20}+...+\frac{1}{95.100}\right)\)
\(=\frac{1}{5}.\left(\frac{1}{5}-\frac{1}{10}+\frac{1}{10}-\frac{1}{15}+\frac{1}{15}-\frac{1}{20}+...+\frac{1}{95}-\frac{1}{100}\right)\)
\(=\frac{1}{5}.\frac{19}{100}=\frac{19}{500}\)
\(\frac{1}{5.10}+\frac{1}{10.15}+\frac{1}{15.20}+\frac{1}{20.25}+...+\frac{1}{95.100}\)
\(=1-\frac{1}{5}+\frac{1}{5}-\frac{1}{10}+\frac{1}{10}-\frac{1}{15}+\frac{1}{15}-\frac{1}{20}+...+\frac{1}{95}-\frac{1}{100}+\frac{1}{100}\)
\(=1-\frac{1}{100}\)
\(=\frac{99}{100}\)
Nếu thấy đứng thì tích nha
Đặt A = 1/5x10 + 1/10x15 + 1/15x20 + 1/20x25 + ... + 1/95x100
A x 5 = 5/5x10 + 5/10x15 + 5/15x20 + 5/20x25 + ... + 5/95x100
A x 5 = 1/5 - 1/10 + 1/10 - 1/15 + 1/15 - 1/20 + 1/20 - 1/25 + ... + 1/95 - 1/100
A x 5 = 1/5 - 1/100
A x 5 = 19/100
A = 19/100 : 5
A = 19/100 x 1/5
A = 19/500
Vậy A= 19/500
\(\frac{1}{5.10}+...+\frac{1}{95.100}\)
\(=\frac{1}{5}\left(\frac{5}{5.10}+...+\frac{5}{95.100}\right)\)
\(=\frac{1}{5}\left(\frac{1}{5}-\frac{1}{100}\right)\)
\(=\frac{1}{5}.\frac{19}{20}\)
\(=\frac{19}{100}\)
pn Tuấn Minh lm đúng r đấy , nhưng mk ik
