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

= 1/2 x ( 3/4 + 1/4 ) 
= 1/2 x 1 
= 1/2
Nếu như thấy thuận tiện thì cho mình 1 nhé. Thanks

= 1/2 * (3/4 + 1/4)

= 1/2 * 4/4

= 1/2 * 1

= 1/2

`#3107.101107`

b)

\(0,5\times\dfrac{3}{4}-\dfrac{1}{2}\times\dfrac{1}{4}\\ =\dfrac{1}{2}\times\dfrac{3}{4}-\dfrac{1}{2}\times\dfrac{1}{4}\\ =\dfrac{1}{2}\times\left(\dfrac{3}{4}-\dfrac{1}{4}\right)\\=\dfrac{1}{2}\times\dfrac{1}{2}\\ =\dfrac{1}{4}\)

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

tự làm

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

\(=\frac{1}{5}\)

=1/2x 2/3x  3/4x 4/5

=1/5

hok tốt 

1/5 học tốt

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

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

\(=\frac{1.2.3.4}{2.3.4.5}\)

\(=\frac{1}{5}\)

( 1 + 1/2 ) . ( 1+ 1/3) . ( 1+ 1/4 ) . ( 1+ 1/5 ) 

=3/2 . 4/3.5/4.6/5

= 3.4.5.6/2.3.4.5

=6/2 = 3 

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

= 1 x \(\dfrac{77}{60}\)

= \(\dfrac{77}{60}\)

a)\(\left(1+\frac{1}{2}\right)\left(1+\frac{1}{3}\right)\left(1+\frac{1}{4}\right)=\frac{3}{2}\cdot\frac{4}{3}\cdot\frac{5}{4}=\frac{3.4.5}{2.3.4}=\frac{5}{2}\)

b)\(\left(1-\frac{1}{2}\right)\left(1-\frac{1}{3}\right)\left(1-\frac{1}{4}\right)=\frac{1}{2}\cdot\frac{2}{3}\cdot\frac{3}{4}=\frac{1.2.3}{2.3.4}=\frac{1}{4}\)

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

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

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

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

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