Question

Tính nhanh M=\(\frac{6}{15.18}\)+\(\frac{6}{18.21}\)+\(\frac{6}{21.24}\)+........+\(\frac{6}{87.90}\)

Answer 1

\(M=\frac{6}{15.18}+\frac{6}{18.21}+\frac{6}{21.24}+.....+\frac{6}{87.90}\)

\(\Rightarrow M=6\left(\frac{1}{15.18}+\frac{1}{18.21}+\frac{1}{21.24}+....+\frac{1}{87.90}\right)\)

\(\Rightarrow M=6\left[\frac{1}{3}\left(\frac{1}{15}-\frac{1}{18}+\frac{1}{18}-\frac{1}{21}+\frac{1}{21}-\frac{1}{24}+.....+\frac{1}{87}-\frac{1}{90}\right)\right]\)

\(\Rightarrow M=6\left[\frac{1}{3}\left(\frac{1}{15}-\frac{1}{90}\right)\right]\Rightarrow M=6\left(\frac{1}{3}.\frac{1}{18}\right)\Rightarrow M=6.\frac{1}{54}\Rightarrow M=\frac{1}{9}\)

Answer 2

Kết quả là : \(\frac{2}{18}\)

   Ngại viết quá ! k nha!

  ^_^ 

Answer 3

1/9 nha bn

Answer 4

M=2(\(\frac{3}{15.18}\)+\(\frac{3}{18.21}\)+\(\frac{3}{21.24}\)+.......+\(\frac{3}{87.90}\))

M=2(\(\frac{1}{15}\)-\(\frac{1}{18}\)+\(\frac{1}{18}\)\(-\frac{1}{21}+\frac{1}{21}-\frac{1}{24}+....+\frac{1}{87}-\frac{1}{90}\)

M=2(\(\frac{1}{15}-\frac{1}{90}\))

M=2.\(\frac{1}{18}\)

M=\(\frac{1}{9}\)

kq =1/9 ,h nha

Answer 5

tích cho mk nha ,kq đúng lắm đó