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a) \(\dfrac{1,28}{3,15}=\dfrac{128}{315}\)
b) \(\dfrac{2}{5}:3\dfrac{1}{4}=\dfrac{2}{5}:\dfrac{13}{4}=\dfrac{2}{5}\cdot\dfrac{4}{13}=\dfrac{8}{65}\)
c) \(\left(-1\dfrac{3}{7}\right):1,24=\dfrac{-10}{7}:\dfrac{31}{25}=\dfrac{-10}{7}\cdot\dfrac{25}{31}=\dfrac{-250}{217}\)
d) \(2\dfrac{1}{5}:3\dfrac{1}{7}=\dfrac{11}{5}:\dfrac{22}{7}=\dfrac{11}{5}\cdot\dfrac{7}{22}=\dfrac{7}{10}\)
a, 26/x + 3 nguyên
=> 26 ⋮ x + 3
=> x + 3 thuộc Ư(26)
=> x + 3 thuộc {-1; 1; -2; 2; -13; 13; -26; 26}
=> x thuộc {-4; -2; -5; -1; -16; 10; -29; 23}
vậy_
b, x+6/x+1 nguyên
=> x + 6 ⋮ x + 1
=> x + 1 + 5 ⋮ x + 1
=> 5 ⋮ x + 1
=> x + 1 thuộc Ư(5)
=> x + 1 thuộc {-1; 1; -5; 5}
=> x thuộc {-2; 0; -6; 4}
vậy_
c, x-2/x+3 nguyên
=> x - 2 ⋮ x + 3
=> x + 3 - 5 ⋮ x + 3
=> 5 ⋮ x + 3
=> x + 3 thuộc Ư(5)
=> x + 3 thuộc {-1; 1; -5; 5}
=> x thuộc {-4; -2; -8; 2}
vậy_
\(a,\frac{26}{x+3}\in Z\Leftrightarrow26\)\(⋮\)\(x+3\)\(\Rightarrow x+3\inƯ_{26}\)
Mà \(Ư_{26}=\left\{\pm1;\pm2;\pm13;\pm26\right\}\)\(\Rightarrow...\)
\(b,\frac{x+6}{x+1}=\frac{x+1+5}{x+1}=1+\frac{5}{x+1}\)
\(\frac{5}{x+1}\in Z\Leftrightarrow5\)\(⋮\)\(x+1\Rightarrow x+1\inƯ_5\)
MÀ \(Ư_5=\left\{\pm1;\pm5\right\}\)\(\Rightarrow...\)
\(c,\frac{x-2}{x+3}=\frac{x+3-3-2}{x+3}=1-\frac{5}{x+3}\)
\(\frac{5}{x+3}\in Z\Leftrightarrow\)\(5\)\(⋮\)\(x+3\Rightarrow x+3\inƯ_5\)
Mà \(Ư_5=\left\{\pm1;\pm5\right\}\)\(\Rightarrow...\)
\(A=-7+\frac{3}{4}-\frac{1}{3}-6+\frac{5}{4}-\frac{4}{3}-3-\frac{7}{4}+\frac{5}{3}\)
\(A=\left(-7-6-3\right)+\left(\frac{3}{4}+\frac{5}{4}-\frac{7}{4}\right)+\left(\frac{5}{3}-\frac{1}{3}-\frac{4}{3}\right)\)
\(A=-16+\frac{1}{4}+0\)
\(A=-15\frac{3}{4}\)
\(A=\left(-7+\frac{3}{4}-\frac{1}{3}\right)-\left(6-\frac{5}{4}+\frac{4}{3}\right)-\left(3+\frac{7}{4}-\frac{5}{3}\right)\)
\(=-7+\frac{3}{4}-\frac{1}{3}-6+\frac{5}{4}-\frac{4}{3}-3-\frac{7}{4}+\frac{5}{3}\)
\(=\left(-7-6-3\right)+\left(\frac{3}{4}+\frac{5}{4}-\frac{7}{4}\right)+\left(\frac{-1}{3}-\frac{4}{3}+\frac{5}{3}\right)\)
\(=-16-\frac{1}{4}\)
Bài làm:
\(\frac{1,28}{3,15}=\frac{128}{315}\)
\(\frac{2}{5}:3\frac{1}{4}=\frac{8}{65}\)
\(\left(-1\frac{3}{7}\right):1,24=-\frac{250}{217}\)
\(2\frac{1}{\frac{5}{3\frac{1}{7}}}=\frac{92}{35}\)