tính nhanh
a)a=2/3x5+2/5x7+2/7x9+...+2/37x39
b)(17/28+18.29+19/30+30/31)x(-5/12+1/4+1/6)
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\(\frac{9^{14}.25^5.8^7}{8^{12}.615^3.25^3}\)
\(=\frac{\left(3^3\right)^{14}.\left(5^2\right)^5.8^7}{8^{12}.\left(3.5.41\right)^3.\left(5^2\right)^3}\)
\(=\frac{3^{42}.5^{10}.8^7}{8^{12}.3^3.5^7.41^3}\)
\(=\frac{3^{39}.5^3}{8^5.41^3}\)
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
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
\(\frac{60}{21}=2\frac{18}{21}\) \(\frac{45}{14}=3\frac{3}{14}\) \(\frac{123}{11}=11\frac{2}{11}\) \(\frac{139}{13}=10\frac{9}{13}\)
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) \(\left(\frac{17}{28}+18.29+\frac{19}{30}+\frac{30}{31}\right)x\left(\frac{-5}{12}+\frac{1}{4}+\frac{1}{6}\right)\)
\(=\left(\frac{17}{28}+18.29+\frac{19}{30}+\frac{30}{31}\right)x0\)
\(=0\)