đáp án 1/6

Đặt A  = 1 - 1/2 + 1 - 1/6 + 1 - 1/12 + 1 - 1/20 + 1 - 1/30 + 1 - 1/42 + 1 - 1/56 + 1 - 1/72 + 1 - 1/89
=  (1 + 1 + 1 + .... 1 + 1) + (1/2 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56 + 1/72 + 1/90)
= 9 - (1/1x2 + 1/2x3 + 1/3x4 + 1/4x5 + 1/5x6 + 1/6x7 + 1/7x8 + 1/8x9 + 1/9x10)
Mỗi phân số thành phần trong biểu thức () ta tách được như sau:
   1/1 x 2 = 1- 1/2
   1/2 x 3 = 1/2 - 1/3

 1/3 x 4 = 1/3 - 1/4
   ........
   1/9 x 10 = 1/9 - 1/10
Như vậy:
A  = 9 - (1-1/2 + 1/2-1/3 + 1/3-1/4 + 1/4-1/5 + 1/5-1/6 + 1/6-1/7 + 1/7-1/8 + 1/8-1/9 + 1/9-1/10)

  = 9 - (1 - 1/10)
    = 9 - 9/10
    = 81/10
                                               Đáp số: 81/10

\(\left(1-\frac{1}{2}\right)x\left(1-\frac{1}{3}\right)x\left(1-\frac{1}{4}\right)x\left(1-\frac{1}{5}\right)x\)\(\left(1-\frac{1}{6}\right)\)

=\(\frac{1}{2}x\frac{2}{3}x\frac{3}{4}x\frac{4}{5}x\frac{5}{6}\)

=\(\frac{1x2x3x4x5}{2x3x4x5x6}\)

=\(\frac{1}{6}\)

1/6

\(=\dfrac{1}{2}\cdot\dfrac{2}{3}\cdot\dfrac{3}{4}\cdot\dfrac{4}{5}\cdot\dfrac{5}{6}=\dfrac{1.2.3.4.5}{2.3.4.5.6}=\dfrac{1}{6}\)

\(\dfrac{1}{6}\)

( 1- \(\frac{1}{2}\))x( 1- \(\frac{1}{3}\))x( 1- \(\frac{1}{4}\))x( 1- \(\frac{1}{5}\))x( 1- \(\frac{1}{6}\)).

= \(\frac{1}{2}\)x \(\frac{2}{3}\)x \(\frac{3}{4}\)x \(\frac{4}{5}\)x \(\frac{5}{6}\).

= \(\frac{1\times2\times3\times4\times5}{2\times3\times4\times5\times6}\).

= \(\frac{1}{6}\).

Ăn có ...chơi có. ...

=1/2*2/3*3/4*4/5*5/6

bn gạch các số có cùng tử số và mẫu số đi

=1/6

ai k mk thì mk k lại

chưa hiểu đề lắm bạn ơi, làm rõ chút nha

\(\frac{1}{6}\)

\(=\dfrac{1}{2}\cdot\dfrac{2}{3}\cdot\dfrac{3}{4}\cdot\dfrac{4}{5}\\ =\dfrac{1}{5}\)

1) 3/9 + 5/9 = 8/9

2) 1/2 x 2/3 x 3/4 x 4/5

= 1/5

(1-1/2)×(1-1/3)×(1-1/4)×(1-1/5)×1-1/6=1/2×2/3×3/4×4/5×5/6=1/6

\(\left(1-\frac{1}{2}\right)\times\left(1-\frac{1}{3}\right)\times\left(1-\frac{1}{4}\right)\times\left(1-\frac{1}{5}\right)=\frac{1}{2}\times\frac{2}{3}\times\frac{3}{4}\times\frac{4}{5}=\frac{1}{5}\)

tự làm

5,5 + \(\dfrac{3}{4}\) - 5 + \(\dfrac{1}{4}\)

(5,5 - 5) + (\(\dfrac{3}{4}\) + \(\dfrac{1}{4}\))

= 0,5  + 1

= 1,5 

\(\dfrac{5}{2}\) x  \(\dfrac{2}{3}\) + \(\dfrac{1}{4}\) : \(\dfrac{3}{2}\)

= \(\dfrac{5}{2}\) x \(\dfrac{2}{3}\) + \(\dfrac{1}{4}\) x \(\dfrac{2}{3}\)

=  (\(\dfrac{5}{2}\) + \(\dfrac{1}{4}\)) x \(\dfrac{2}{3}\)

= (\(\dfrac{10}{4}\) + \(\dfrac{1}{4}\)) x \(\dfrac{2}{3}\)

= \(\dfrac{11}{4}\) x \(\dfrac{2}{3}\)

= \(\dfrac{11}{6}\) 

Tính \(x\): 

  435  - [\(x\) + 16] = 425 : 17

  435 - [\(x\) + 16] = 25

          [\(x\) + 16] = 435 - 25

           \(x\) + 16 = 410

           \(x\)        = 410 - 16

          \(x\)         = 394

\(x\) x \(\dfrac{1}{4}\) - \(\dfrac{3}{4}\) = 6 : \(\dfrac{3}{4}\)

\(x\) \(\times\) \(\dfrac{1}{4}\) - \(\dfrac{3}{4}\) = 6 x \(\dfrac{4}{3}\)

\(x\) x \(\dfrac{1}{4}\) - \(\dfrac{3}{4}\)  = 8

\(x\) x \(\dfrac{1}{4}\)        = 8 + \(\dfrac{3}{4}\)

\(x\) x \(\dfrac{1}{4}\)        = \(\dfrac{32}{4}\) + \(\dfrac{3}{4}\)

\(x\) x \(\dfrac{1}{4}\)       = \(\dfrac{35}{4}\)

\(x\)              =  \(\dfrac{35}{4}\) : \(\dfrac{1}{4}\)

\(x\)              = \(\dfrac{35}{4}\) x 4

\(x\)             = 35

Tui rất cảm ơn b nhiều :))))