Câu 14:
a: \(\frac79-\frac29=\frac{7-2}{9}=\frac59\)
b: \(-\frac{9}{11}\cdot\frac52=\frac{-9\cdot5}{11\cdot2}=\frac{-45}{22}\)
c: \(-\frac34\cdot\frac{16}{17}=\frac{-3}{17}\cdot\frac{16}{4}=\frac{-3}{17}\cdot4=-\frac{12}{17}\)
d: \(\frac95:\frac{-3}{5}=\frac95\cdot\frac{5}{-3}=\frac{9}{-3}=-3\)
e: \(\frac27:\frac{-5}{14}=\frac27\cdot\frac{14}{-5}=\frac{2\cdot2}{-5}=\frac{-4}{5}\)
f: \(\frac57\cdot\frac{5}{11}+\frac57\cdot\frac{2}{11}-\frac57\cdot\frac{14}{11}\)
\(=\frac57\left(\frac{5}{11}+\frac{2}{11}-\frac{14}{11}\right)\)
\(=\frac57\cdot\frac{-7}{11}=-\frac{5}{11}\)
g: \(\frac{7}{19}\cdot\frac{8}{11}+\frac{7}{19}\cdot\frac{3}{11}+\frac{12}{19}\)
\(=\frac{7}{19}\left(\frac{8}{11}+\frac{3}{11}\right)+\frac{12}{19}\)
\(=\frac{7}{19}+\frac{12}{19}=\frac{19}{19}=1\)
h: \(1,5\cdot\frac{11}{9}-\left(\frac45+\frac23\right):2\frac15\)
\(=\frac{11}{6}-\left(\frac{12}{15}+\frac{10}{15}\right):\frac{11}{5}\)
\(=\frac{11}{6}-\frac{22}{15}\cdot\frac{5}{11}=\frac{11}{6}-\frac23=\frac{11}{6}-\frac46=\frac76\)
Câu 15:
a: \(x-\frac34=\frac12\)
=>\(x=\frac34+\frac12=\frac54\)
b: \(x:\frac{8}{11}=\frac{11}{3}\)
=>\(x=\frac{11}{3}\cdot\frac{8}{11}=\frac83\)
c: \(\left(2,8x-32\right):\frac23=-90\)
=>\(2,8x-32=-90\cdot\frac23=-60\)
=>2,8x=-28
=>x=-10
