Bài 4:
Ba người làm chung thì:
\(1:\left(\dfrac{1}{3}+\dfrac{1}{6}+\dfrac{1}{8}\right)=1.6\left(h\right)\)
3.\(ĐK:x\in N;x\ne2\)
\(\dfrac{n+7}{n-2}=\dfrac{n-2+9}{n-2}=\dfrac{n-2}{n-2}+\dfrac{9}{n-2}=1+\dfrac{9}{n-2}\)
Để \(\dfrac{n+7}{n-2}\in Z\) thì \(9⋮n-2\) hay \(n-2\in U\left(9\right)=\left\{\pm1;\pm3;\pm9\right\}\)
Xét: n-2=1 =>n=3 (tm)
n-2=-1=>n=1(tm)
n-2=3=>n=5(tm)
n-2=-3=>n=-1(ktm)
n-2=9=>n=11(tm)
n-2=-9=>n=-7(ktm)
Vậy \(n=\left\{1;3;5;11\right\}\)
1.
a.\(A=\left[25+\dfrac{19}{36}:\dfrac{19}{6}\right].0,4=\left[25+\dfrac{1}{6}\right].\dfrac{2}{5}=\dfrac{151}{6}.\dfrac{2}{5}=\dfrac{151}{15}\)
b.\(B=\dfrac{21}{5}+\left|-\dfrac{5}{14}\right|.\dfrac{14}{15}=\dfrac{21}{5}+\dfrac{5}{14}.\dfrac{14}{15}=\dfrac{21}{5}+\dfrac{1}{3}=\dfrac{68}{15}\)
2.
a.\(\Leftrightarrow-\dfrac{13}{12}< x\le2\) \(\Leftrightarrow x=-1;x=0;x=1;x=2\)
b.\(\Leftrightarrow\dfrac{1}{2}x-\dfrac{3}{8}-\dfrac{2}{5}x=\dfrac{17}{4}\)
\(\Leftrightarrow\dfrac{1}{10}x=\dfrac{37}{8}\) \(\Leftrightarrow x=\dfrac{185}{4}\)
