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a) (-5). x = 15
Dự đoán: x = -3
Kiểm tra: (-5). (-3) = 15
b) x . (-8) = - 56
Dự đoán: x = 7
Kiểm tra: 7. (-8) = - 56
c) 6. x = -42
Dự đoán: x = -7
Kiểm tra: 6. (-7) = -42
d) x .(-9) = 54
Dự đoán: x = - 6
Kiểm tra (-6) .(-9) = 54
a) x= 1/4
b) x= -7/144
c) x= 25/6
d) x=17/7
e) x= 80/63
f) x= -45/14
\(a.\)
\(\frac{4}{9}.x=\frac{1}{9}\)
\(\Rightarrow x=\frac{1}{9}:\frac{4}{9}\)
\(\Rightarrow x=\frac{1}{9}.\frac{9}{4}\)
\(\Rightarrow x=\frac{1}{4}\)
Vậy \(x=\frac{1}{4}\)
\(b.\)
\(\frac{7}{18}.x-\frac{2}{3}=\frac{5}{18}\)
\(\Rightarrow\frac{7}{18}.x=\frac{5}{18}+\frac{2}{3}\)
\(\Rightarrow\frac{7}{18}.x=\frac{5}{18}+\frac{12}{18}\)
\(\Rightarrow\frac{7}{18}.x=\frac{17}{18}\)
\(\Rightarrow x=\frac{17}{18}:\frac{7}{18}\)
\(\Rightarrow x=\frac{17}{18}.\frac{18}{7}\)
\(\Rightarrow x=\frac{17}{7}\)
Vậy \(x=\frac{17}{7}\)
\(c.\)
\(x:-\frac{1}{12}=\frac{7}{12}\)
\(\Rightarrow x=\frac{7}{12}.-\frac{1}{12}\)
\(\Rightarrow x=-\frac{7}{144}\)
Vậy \(x=-\frac{7}{144}\)
\(d.\)
\(\frac{4}{9}-\frac{7}{8}.x=-\frac{2}{3}\)
\(\Rightarrow\frac{7}{8}.x=\frac{4}{9}-\left(-\frac{2}{3}\right)\)
\(\Rightarrow\frac{7}{8}.x=\frac{4}{9}+\frac{2}{3}\)
\(\Rightarrow\frac{7}{8}.x=\frac{4}{9}+\frac{6}{9}\)
\(\Rightarrow\frac{7}{8}.x=\frac{10}{9}\)
\(\Rightarrow x=\frac{10}{9}:\frac{7}{8}\)
\(\Rightarrow x=\frac{10}{9}.\frac{8}{7}\)
\(\Rightarrow x=\frac{80}{63}\)
Vây \(x=\frac{80}{63}\)
\(e.\)
\(-\frac{5}{14}:x=-\frac{3}{10}\)
\(\Rightarrow x=-\frac{5}{14}:-\frac{3}{10}\)
\(\Rightarrow x=-\frac{5}{14}.-\frac{10}{3}\)
\(\Rightarrow x=\frac{5}{7}.\frac{5}{3}\)
\(\Rightarrow x=\frac{25}{21}\)
Vậy \(x=\frac{25}{21}\)
\(g.\)
\(\frac{1}{6}+\frac{-5}{7}:x=-\frac{7}{18}\)
\(\Rightarrow-\frac{5}{7}:x=-\frac{7}{18}-\frac{1}{6}\)
\(\Rightarrow-\frac{5}{7}:x=-\frac{7}{18}-\frac{3}{18}\)
\(\Rightarrow-\frac{5}{7}:x=-\frac{10}{18}\)
\(\Rightarrow-\frac{5}{7}:x=-\frac{5}{9}\)
\(\Rightarrow x=-\frac{5}{7}:-\frac{5}{9}\)
\(\Rightarrow x=-\frac{5}{7}.-\frac{9}{5}\)
\(\Rightarrow x=\frac{9}{7}\)
Vậy \(x=\frac{9}{7}\)
