Bài làm
\(M=\frac{3^2}{2.5}+\frac{3^2}{5.8}+\frac{3^2}{8.11}+...+\frac{3^2}{98.101}\)
\(M=3^2\left(\frac{1}{2.5}+\frac{1}{5.8}+\frac{1}{8.11}+...+\frac{1}{98.101}\right)\)
\(M=9.\left(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+...+\frac{1}{98}-\frac{1}{101}\right)\)
\(M=9\left(\frac{1}{2}-\frac{1}{101}\right)\)
\(M=9.\left(\frac{101}{202}-\frac{2}{202}\right)\)
\(M=9.\frac{99}{202}\)
\(M=\frac{891}{202}\)
Vậy \(M=\frac{891}{202}\)
M= 3.(3/2.5+ 3/5.8.....3/98.101)
= 3.( 1/2-1/5+1/5-1/8 +....+1/98-1/101)
=3.( 1/2-1/101)
= 3.( 101/202- 2/202)
=3. 99/202
= 297/202
Vậy M= 297/202 nha bạn
