Mk bik câu B nè!

2B = 2/3.5 + 2/5.7 + 2/7.9 +.......+2/97.99

2B = 1/3 - 1/5 + 1/5 - 1/7 +.......+ 1/97 - 1/99

2B = 1/3 - 1/99

2B = 32/99

=> B = 16/99 

Bạn có chắc là đúng ko vậy

bài A sai đề rồi bạn coi lại đi

B=1/3.5+1/5.7+1/7.9+...........+1/97.99

B=1.2/2.3.5+1.2/2.5.7+1.2/2.7.9+...+1.2/2.97.99

B=1/2.2/3.5+1/2.2/5.7+1/2.2/7.9+...+1/2.2/97.99

B=1/2(1/3.5+1/5.7+1/7.9+...+1/97.99)

B=1/2(1/3-1/5+1/5-1/7+1/7-1/9+...+1/97-1/99)    (dùng phương pháp khử)

B=1/2(1/3-1/99)

B=1/2.32/99

B=16/99

\(M=\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{97.99}\)\(\)

\(M=\frac{2}{3}-\frac{2}{5}+\frac{2}{5}-\frac{2}{7}+...+\frac{2}{97}-\frac{2}{99}\)

\(M=\frac{2}{3}-\frac{2}{99}\)

\(M=\frac{64}{99}\)

\(2M=\left(\frac{2}{3}-\frac{2}{5}\right)+\left(\frac{2}{5}-\frac{2}{7}\right)+\left(\frac{2}{7}-\frac{2}{9}\right)+...+\left(\frac{2}{97}-\frac{2}{99}\right)\)

\(2M=\frac{2}{3}-\frac{2}{5}+\frac{2}{5}-\frac{2}{7}+\frac{2}{7}-\frac{2}{9}+...+\frac{2}{97}-\frac{2}{99}\)

\(2M=\frac{2}{3}-\left(\frac{2}{5}-\frac{2}{5}\right)-\left(\frac{2}{7}-\frac{2}{7}\right)-...-\left(\frac{2}{97}-\frac{2}{97}\right)-\frac{2}{99}\)

\(2M=\frac{2}{3}-\frac{2}{99}\)

\(2M=\frac{64}{99}\)

\(M=\frac{32}{99}\)

k mình nha mình đang cần

\(=2\cdot\left(\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+...+\dfrac{1}{97}-\dfrac{1}{99}+\dfrac{1}{99}-\dfrac{1}{101}\right)\)

\(=2\cdot\left(\dfrac{1}{3}-\dfrac{1}{101}\right)=2\cdot\dfrac{98}{303}=\dfrac{196}{303}\)

= 2/3 . 2/5 + 2/5 . 2/7 + ... + 2/99 . 2/101

= 2/3 - 2/5 + 2/5 - 2/7 + ... + 2/99 - 2/101

= 2/3 - 2/101

= 196/303

2/3 - 2/5 + 2/5 - 2/7 + 2/7 - 2/9 + .... + 2/97 - 2/99 + 2/99 - 2/101

 = 2/3 - 2/101

= 196/303

M = 1/3 - 1/5 + 1/5 - 1/7 + 1/7 - 1/9 + ..... + 1/97 - 1/99

M = 1/3 - 1/99

M = 32/99

M=1/3-1/5+1/5-1/7+1/7-1/9+...+1/97-1/99

=1/3-1/99

=32/99

Ta có M= 2/3*5+2/5*7+2/7*9+...+2/97*99

            = 1/3-1/5+1/5-1/7+1/7-1/9+...+1/97-1/99

            = 1/3+(1/5-1/5)+(1/7-1/7)+...+(1/97-1/97)-1/99

            = 1/3 - 1/99

            = 32/99

Vậy M= 32/99

\(\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+...+\frac{2}{97.99}\)

\(=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{97}-\frac{1}{99}\)

\(=\frac{1}{3}+\left(\frac{1}{5}-\frac{1}{5}\right)+\left(\frac{1}{7}-\frac{1}{7}\right)+...+\left(\frac{1}{97}-\frac{1}{97}\right)-\frac{1}{99}\)

\(=\frac{1}{3}-\frac{1}{99}=\frac{32}{99}\)

~ Hok tốt ~

\(\)

Viết thành 2 . (1/3.5 + 1/5.7 + 1/7.9 + ...+ 1/97.99

Tui hk bít nữa

\(M=\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+...+\frac{1}{97.99}\)

\(\Rightarrow M=\frac{1}{2}\left(\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+...+\frac{2}{97.99}\right)\)

\(\Rightarrow M=\frac{1}{2}\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{97}-\frac{1}{99}\right)\)

\(\Rightarrow M=\frac{1}{2}\left(\frac{1}{3}-\frac{1}{99}\right)\)

\(\Rightarrow M=\frac{1}{2}.\frac{32}{99}\)

\(\Rightarrow M=\frac{16}{99}\)

\(M=\frac{1}{3.5}+\frac{1}{5.7}+...+\frac{1}{97.99}\)

\(M=\frac{1}{2}\left(\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{97.99}\right)\)

\(M=\frac{1}{2}.\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5.}-\frac{1}{7}+...+\frac{1}{97}-\frac{1}{99}\right)\)

\(M=\frac{1}{2}.\left(\frac{1}{3}-\frac{1}{99}\right)=\frac{16}{99}\)

nhân M với 2  

c/m theo công thức ta được

10M=1/3-1/99

10M=32/99

M=16/495

dung thi tk nhâ

Bài làm:

Ta có: Đặt \(A=\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+...+\frac{2}{97.99}\)

\(A=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{97}-\frac{1}{99}\)

\(A=\frac{1}{3}-\frac{1}{99}=\frac{32}{99}>\frac{32}{100}=32\%\)

=> Biểu thức trên > 32%

=> đpcm

Dạ đề nghị bạn Vũ Ngọc Tuấn không spam linh tinh lên bài làm nữa nhé!

Ta có:

\(\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{97.99}=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{97}-\frac{1}{99}=\frac{1}{3}-\frac{1}{99}=\frac{32}{99}>\frac{32}{100}\)= 32%

M=\(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{97}-\frac{1}{99}\)

M=\(\frac{1}{3}-\frac{1}{99}\)

M=\(\frac{32}{99}\)

TICK ỦNG HỘ NHA