`@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`

a: \(=60\cdot\dfrac{17}{20}=51\)

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

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

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

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

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

1 + 1 x 1 +1 = 1 + 1 +1 = 3
2 + 2 x 2 +2 = 2 + 4 + 2 = 8
3 + 3 - 3 + 3 = 6 - 3 + 3 = 6
4 - 4 + 4 - 4 = 0 + 4 - 4 = 0
5 x 5 - 5 x 5 = 25 - 25 =0
1 + 1 + 2 + 3 + 4 + 5 = 16
1 x 1 x 2 x 3 x 4 x 5 = 120

1 + 1 x 1 + 1 = 3

2 + 2 x 2 + 2 = 8

3 + 3 x 3 + 3 = 15

4 - 4 + 4 - 4 = 0

5 x 5 - 5 x 5 = 0

1 + 1 + 2 + 3 + 4 + 5 =16

1 x 1 x 2 x 3 x 4 x 5 = 120

k nh

1 + 1 * 1 + 1 = 1 + 1 + 1 = 3

2 + 2 * 2 + 2 = 2 + 4 + 2 = 8

3 + 3 - 3 + 3 = 6 - 3 + 3 = 3 + 3 = 6

4 - 4 + 4 - 4 = 0 + 4 - 4 = 4 -4 = 0

5 * 5 - 5 * 5 = 25 - 25 = 0

1 + 1 + 2 + 3 + 4 + 5 = 2 + 2 + 3 + 4 + 5 = 4 + 3 + 4 + 5 = 7 + 4 + 5 =11 + 5 = 16

1 * 1 * 2 * 3 * 4 * 5 = 120

Nhớ k cho mk nha !!

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

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

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

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

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

\(\left(1+\frac{1}{2}\right)\cdot\left(1+\frac{1}{3}\right)\cdot...\cdot\left(1+\frac{1}{2010}\right)\)

\(=\frac{3}{2}\cdot\frac{4}{3}\cdot\frac{5}{4}\cdot...\cdot\frac{2011}{2010}\)

\(=\frac{2011}{2}\)

\(=1005,5\)

Lớp 8 đâu?

lp 6 đâu

lớp 6 đâu

Tìm y biết 3 x y x (1/1 x 1/2 + 1/2 x 1/3 + 1/3 x 1/4 + 1/4 x 1/5 + 1/5 x 1/6) = 3/4

Ta thấy: 1/1x1/2 = 1/1-1/2  ;  1/2x1/3 = ½-1/3  ;  1/3x1/4=1/3-1/4  ;  1/4x1/5=1/4-1/5  ;  1/5x1/6=1/5-1/6

Nên

1/1 x 1/2 + 1/2 x 1/3 + 1/3 x 1/4 + 1/4 x 1/5 + 1/5 x 1/6 =

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

Hay 3 x y x 5/6 = 3/4

y x 15/6 = 3/4

y= 3/4 : 15/6

y  =  3/10

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