a) \(a=\frac{2}{3\cdot5}+\frac{2}{5\cdot7}+\frac{2}{7\cdot9}+...+\frac{2}{37\cdot39}\)

\(a=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{37}-\frac{1}{39}\)

\(a=\frac{1}{3}-\frac{1}{39}\)

\(a=\frac{12}{39}\)

b) \(\left(\frac{17}{28}+18.29+\frac{19}{30}+\frac{30}{31}\right)\cdot\left(\frac{-5}{12}+\frac{1}{4}+\frac{1}{6}\right)\)

\(=\left(\frac{17}{28}+18.29+\frac{19}{30}+\frac{30}{31}\right)\cdot\left(\frac{-5}{12}+\frac{3}{12}+\frac{2}{12}\right)\)

\(=\left(\frac{17}{28}+18.29+\frac{19}{30}+\frac{30}{31}\right)\cdot\left(\frac{-2}{12}+\frac{2}{12}\right)\)

\(=\left(\frac{17}{28}+18.29+\frac{19}{30}+\frac{30}{31}\right)\cdot0\)

\(=0\)

a) \(A=\frac{2}{3x5}+\frac{2}{5x7}+\frac{2}{7x9}+...+\frac{2}{37x39}\)

\(A=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{37}-\frac{1}{39}\)

\(A=\frac{1}{3}-\frac{1}{39}\)

\(A=\frac{4}{13}\)

b) \(\left(\frac{17}{28}+18.29+\frac{19}{30}+\frac{30}{31}\right)x\left(\frac{-5}{12}+\frac{1}{4}+\frac{1}{6}\right)\)

\(=\left(\frac{17}{28}+18.29+\frac{19}{30}+\frac{30}{31}\right)x0\)

\(=0\)

\(\frac{9^{14}.25^5.8^7}{8^{12}.615^3.25^3}\)

\(=\frac{\left(3^3\right)^{14}.\left(5^2\right)^5.8^7}{8^{12}.\left(3.5.41\right)^3.\left(5^2\right)^3}\)

\(=\frac{3^{42}.5^{10}.8^7}{8^{12}.3^3.5^7.41^3}\)

\(=\frac{3^{39}.5^3}{8^5.41^3}\)

b) Để b là số nguyên

=> 2/n-1 thuộc Z

=> n-1 thuộc Ư(2) = (1;-1;2;-2)

nếu n -1 = 1 => n = 2

n-1=-1 => n = 0

n-1 = 2 => n = 3

n-1 = -2 => n = -1

KL: n = (2;0;3;-1)

a) Để b là phân số

\(\Rightarrow n\ne\left(2;0;3;-1\right)\)

a) 128 - 3 ( x + 4 ) = 23

     3 ( x + 4 ) = 128 - 23

     3 ( x + 4 ) = 105

     x + 4 = 105 : 3

     x + 4 = 35

     x = 35 - 4

     x = 31

Học tốt bạn nhé!!!

Arigatou ^^

b) \(\left(12x-64\right).8^3=4.8^4\)

\(\left(12x-64\right).8^3=32.8^3\)

\(\Rightarrow12x-64=32\)

12x = 32 + 64

12x  = 96

x = 96 : 12

x = 8

trả lời:

a)ta có:

8 = 2^3

9 = 3^2

10 = 2.5

=> BCBN(8,9,10) = 2^3 . 3^2 . 5 = 360

b)

2=2

3 = 3

6 = 2.3

=> BCNN(2,3,6) = 2.3 = 6

học tốt nha hà lan anh><

a) Ta có : 8 = 2³ 

                9 = 3² 

              10 = 2 . 5

BCNN(8; 9; 10) = 2³ . 3² . 5 = 360

b) Ta có : 2 = 2

                3 = 3

                6 = 2 . 3

BCNN(2; 3; 6) = 2 . 3 = 6

x + 25%.x = 125

x + 1/4. x = 125

x. (1+1/4) = 125

x. 5/4 = 125

x = 125:5/4

x = 100

x+25%x=125

=>x(1/4+1)=125

=>x.5/4=125

=>x=125:5/4

=>x=100

Vậy x=100

\(2x+3x=10\)

\(\left(2+3\right)\cdot x=10\)

\(5x=10\)

\(x=10:5\)

\(x=2\)

Học tốt nhé bạn

2x+3x=10

5x=10

x=2

trả lời :

6,1 m2 = 0,00061 ha

hok tốt !!!

Trả lời:

6,1 m2 = 0,00061 ha

Bài 1:

a. \(\frac{315}{100}=3\frac{3}{20}\)                         \(\frac{89}{10}=8\frac{9}{10}\)                           \(\frac{124}{50}=2\frac{12}{25}\)                       \(\frac{100}{24}=4\frac{1}{6}\)

b. \(\frac{60}{21}=2\frac{6}{7}\)                              \(\frac{45}{14}=3\frac{3}{14}\)                           \(\frac{123}{11}=11\frac{2}{11}\)                      \(\frac{139}{13}=10\frac{9}{13}\)

1.a,\(\frac{315}{100}\)=\(\frac{300}{100}+\frac{15}{100}=3+\frac{15}{100}=3\frac{15}{100}\)     ;   \(\frac{89}{10}=\frac{80}{10}+\frac{9}{10}=8+\frac{9}{10}=8\frac{9}{10}\)

\(\frac{124}{50}=\frac{100}{50}+\frac{24}{50}=2+\frac{24}{50}=2\frac{24}{50}\)               ;   \(\frac{100}{24}=\frac{96}{24}+\frac{4}{24}=4+\frac{4}{24}=4\frac{4}{24}\)

b, tương tự trên mình làm ngắn hơn nha

\(\frac{60}{21}=2\frac{18}{21}\)     \(\frac{45}{14}=3\frac{3}{14}\)   \(\frac{123}{11}=11\frac{2}{11}\)  \(\frac{139}{13}=10\frac{9}{13}\)