a,

=1/2x2/3x3/4x...x17/18x18/19x19/20

=1/20

b,

co dung ko day ban

a) 2/9 : 2/3 x 1/2

= 2/9 x 3/2 x 1/2

= 6/18 x 1/2

= 6/36

b) 2 + 1/4 x 4/3

= 2 + 4/7

= 2/1₍₇₎ + 4/7

= 14/7 + 4/7

= 18/7

c) 3 x 1/2 x 1/4

= 3/1 x 1/2 x 1/4

= 3/2 x 1/4

= 3/8

#Hok_tốt

Thông báo,Te2qAMq.png (1280×800)

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\(1\frac12\cdot1\frac13\cdot1\frac14\)

\(=\frac32\cdot\frac43\cdot\frac54=\frac52\)

5/2

câu 2 đề sai

\(\frac{1}{1}\cdot\frac{1}{2}+\frac{1}{2}\cdot\frac{1}{3}+\frac{1}{3}\cdot\frac{1}{4}+...+\frac{1}{79}\cdot\frac{1}{80}\)

\(=\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{79\cdot80}\)

\(=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}+...+\frac{1}{79}-\frac{1}{80}\)

\(=1-\frac{1}{80}\)

\(=\frac{79}{80}\)

`@Fù`

`=1/(1×2)+1/(2×3)+1/(3×4)+...+1/(72×73)`

`=1/1-1/2+1/2-1/3+...+1/72-1/73`

`=1-1/73`

`=72/73`

tích đúng mình giải cho

= 1/1x2 + 1/2x3 + 1/3x4 + 1/4x5 + 1/5 x 6

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

= 1 - 1/6

= 5/6

nha,mơn nhìu

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

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

\(=1-\frac{1}{6}=\frac{5}{6}\)