Question

A=1/3 + 1/15 + 1/35 + 1/63 +.....+ 1/195

Answer 1

Đặt A = 1/3+1/15+1/35+1/63+1/99+1/143+1/195

2A= 2/﴾1.3﴿ + 2/﴾3.5﴿ + 2/﴾5.7﴿ + 2/﴾7.9﴿+2/﴾9.11﴿ + 2/﴾11.13﴿+2/﴾13.15﴿

2A=1/1‐1/3+1/3‐1/5+1/5‐1/7+1/7‐1/9+1/9...

2A=1/1‐1/15=14/15

Vậy A=14/15 : 2 = 7/15 

Answer 2

A=1/1x3 + 1/3x5 + 1/5x7.......+1/13x15

2A=2/1x3 + 2/3x5 + 2/5x7.......+2/13x15

2A=1-1/3+1/3-1/5+1/5-1/7.......+1/13-1/15

2A=1-1/15

A= 7/15

Answer 3

Đặt A = 1/3+1/15+1/35+1/63+1/99+1/143+1/195

2A= 2/﴾1.3﴿ + 2/﴾3.5﴿ + 2/﴾5.7﴿ + 2/﴾7.9﴿+2/﴾9.11﴿ + 2/﴾11.13﴿+2/﴾13.15﴿

2A=1/1‐1/3+1/3‐1/5+1/5‐1/7+1/7‐1/9+1/9...

2A=1/1‐1/15=14/15

Vậy A=14/15 : 2 = 7/15 

Answer 4

A=1/1.3+1/3.5+1/5.7+...+1/13.15

  =1/2.(2/1.3+2/3.5+1/5.7+...+2/13.15)

  =1/2.(1-1/3+1/3-1/5+...+1/13-1/15)

  =1/2.(1-1/15)

  =1/2.14/15=7/15

Vậy A=7/15

ĐÚNG RÙI ĐÓ BẠN NHỚ

Answer 5

quá dễ!Để  mình làm cho nha hihi

1/3+1/15+1/35+1/63+......+1/195=1-1/195=194/195

Answer 6

=1/1*3 * 2/2 + 1/3*5 * 2/2 + 1/5*7 + 2/2 + 1/7*9 * 2/2 +...+1/13*15 * 2/2

=2/1/3 * 1/2 + 2/3*5 * 1/2 + 2/5*7 * 1/2 + 2/7*9 * 1/2 +...+2/13*15 * 1/2

=1/2 * (2/1*3+ 2/3*5 +2/5*7 + 2/7*9 +...+2/13*15 )

=1/2*(1-1/3+1/3-1/5+1/5-1/7+1/7+1/9+...+1/13-1/15)

=1/2*(1-1/15 )

=1/2*(15/15-1/15)

=1/2*14/15

=7/15