Gọi biểu thức cần tình giá trị là A.

Ta có: \(A=\dfrac{1}{4.8}+\dfrac{1}{8.12}+\dfrac{1}{12.16}+...+\dfrac{1}{2008.2012}\)

\(\Leftrightarrow4A=4\left(\dfrac{1}{4.8}+\dfrac{1}{8.12}+\dfrac{1}{12.16}+...+\dfrac{1}{2008.2012}\right)\)

\(\Leftrightarrow4A=\dfrac{1}{4}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{12}+\dfrac{1}{12}-\dfrac{1}{16}+...+\dfrac{1}{2008}-\dfrac{1}{2012}\)

\(\Leftrightarrow4A=\dfrac{1}{4}-\dfrac{1}{2012}=\dfrac{251}{1006}\)

\(\Leftrightarrow A=\dfrac{\dfrac{251}{1006}}{4}=\dfrac{251}{4024}\)

Ta gọi Biểu thức trên là A ta có:

A= \(\dfrac{1}{4.8}+\dfrac{1}{8.12}+\dfrac{1}{12.16}+...+\dfrac{1}{2008.2012}\)

4.A=\(\dfrac{4}{4.8}+\dfrac{4}{8.12}+\dfrac{4}{12.16}+...+\dfrac{4}{2008.201}\)

4.A=\(\dfrac{1}{4}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{12}+\dfrac{1}{12}-\dfrac{1}{16}+...+\dfrac{1}{2008}-\dfrac{1}{2012}\)

4.A=\(\dfrac{1}{4}-\dfrac{1}{2012}\)

4.A=\(\dfrac{502}{2012}\)

  A=\(\dfrac{502}{2012}:4\)

  A=\(\dfrac{502}{8048}\)

  A=\(\dfrac{251}{4024}\)

  Vậy biểu thức trên có giá trị là \(\dfrac{251}{4024}\)

A = 3 ​(1/3 - 1/5 + 1/5 - 1/8 + 1/8 - 1/12 + 1/12 - 1/17) = 3(1/3 - 1/17) = 14/17

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A = \(\frac{6}{3}.5+\frac{9}{5}.8+\frac{12}{8}.12+\frac{15}{12}.17\)

    \(=3\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{12}+\frac{1}{12}-\frac{1}{17}\right)\)

    \(=3\left(\frac{1}{3}-\frac{1}{17}\right)\)

    \(=3\times\frac{14}{51}\)

    \(=\frac{14}{17}\)

CHÚC BẠN HỌC TỐT !!!

6,18 + 5,15 + 8,12

= 11,33 + 8,12

= 19,45

đáp án là 19,45

Xét tử: 2.4+4.8+8.12+12.16+16.20 = 2.1.2.2 + 2.2.2.4 + 2.2.4.6 + 2.2.6.8 + 2.2.8.10

                                                   = 2.2.(1.2+2.4+4.6+6.8+8.10)

=> 2.4+4.8+8.12+12.16+16.20/1.2+2.4+4.6+6.8+8.10 = 2.2.(1.2+2.4+4.6+6.8+8.10) / 1.2+2.4+4.6+6.8+8.10

                                                                               = 2.2 = 4

camon nhan (:

a, 35.(34+86) +65.(75+45)= 35. 120 +65.120= 120.(35+65)=120.100=12000

a, 35x34+35x86+65x75+65x45

=35x(34+86)+65x(75+45)

=35x120+65x120

=120x(35+65)

=120x100

=12000

b,3x25x8+4x6x37+2x8x12

=24x25+24x37+24x8

=24x(25+37+8)

=24x70

=1680

\(\frac{4^5\cdot25^4-2\cdot10^9}{2^{10}\cdot5^8+10^8\cdot12}=\frac{\left(2^2\right)^5\cdot\left(5^2\right)^4-2\cdot10^8\cdot10}{2^{10}\cdot5^8+10^8\cdot2\cdot6}\)

\(=\frac{2^{10}\cdot5^8-2\cdot10^8\cdot10}{2^{10}\cdot5^8+10^8\cdot2\cdot6}=....\)

Còn lại bn tự lm nha

đáp án = 60 

tích mik nha !!!

962546 nhe