Question

Tính

M=1/4+1/28+1/70+...+1/868

Answer 1

M = 1/4 + 1/28 + 1/70 + ... + 1/868

M = 1/1.4 + 1/4.7 + 1/7.10 + ... + 1/28.31

M = 1/3 . ( 3/1.4 + 3/4.7 + 3/7.10 + .... + 3/28.31 )

M = 1/3 . ( 1 - 1/4 + 1/4 - 1/7 + 1/7 - 1/10 + ... + 1/28 - 1/31 )

M = 1/3 . ( 1 - 1/31 )

M = 1/3 . 30/31

M = 10/31

Answer 2

  M=1/4+1/28+1/70+...+1/868

  M=1/1x4+1/4x7+1/7x10+...+1/28x31

3M=3/1x4+3/4x7+3/7x10+...+3/28x31

3M=1-1/4+1/4-1/7+1/7-1/10+...+1/28-1/31

3M=1-1/31

3M=31/31-1/31

3M=30/31

  M=30/31:3

  M=10/31

 

Answer 3

M=1/1x4+1/4x7+1/7x10+...+1/28x31

M=1/3x(3/1x4+3/4x7+3/7x10+...+3/28x31)

M=1/3x(1-1/4+1/4-1/7+1/7-1/10+...+1/28-1/31)

M=1/3x(1-1/31)

M=1/3x30/31

M=10/31