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a) \(\frac{3}{4}-\frac{1}{6}-\frac{a}{b}=\frac{1}{2}\)
\(\frac{7}{12}-\frac{a}{b}=\frac{1}{2}\)
\(\frac{a}{b}=\frac{7}{12}-\frac{1}{2}\)
\(\frac{a}{b}=\frac{1}{12}\)
b) \(\frac{a}{b}\times\frac{1}{4}\times\frac{2}{5}=\frac{1}{7}\)
\(\frac{a}{b}\times\frac{1}{10}=\frac{1}{7}\)
\(\frac{a}{b}=\frac{1}{7}:\frac{1}{10}\)
\(\frac{a}{b}=\frac{10}{7}\)
c) \(\frac{1}{3}:\frac{a}{b}=\frac{2}{3}:\frac{4}{3}\)
\(\frac{1}{3}:\frac{a}{b}=\frac{1}{2}\)
\(\frac{a}{b}=\frac{1}{3}:\frac{1}{2}\)
\(\frac{a}{b}=\frac{3}{2}\)
6.
\(\dfrac{13}{60}\) và \(\dfrac{7}{30}\)
7.
a = 36
b = 144
Mấy câu khác bạn tự tính nhé, dễ thôi. Câu 2, câu 3 giống dạng nhau. Dấu . có nghĩa là dấu nhân nhé.
Câu 2:
\(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}\)
\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}\)
\(=\frac{1}{2}-\frac{1}{8}\)
\(=\frac{3}{8}\)
Câu 4 b) bạn quy đồng 2 phân số cho cùng mẫu rồi tìm thôi.
Bài 1:
a,Ta có:\(\frac{3}{5}=\frac{3\times2}{5\times2}=\frac{6}{10}\) (1)
\(\frac{4}{5}=\frac{4\times2}{5\times2}=\frac{8}{10}\) (2)
Từ (1) và (2)=> Một phân số tối giản nằm giữa hai phân số trên là:\(\frac{7}{10}\)
b,Ta có:\(\frac{3}{5}=\frac{3\times3}{5\times3}=\frac{9}{15}\)
\(\frac{4}{5}=\frac{4\times3}{5\times3}=\frac{12}{15}\)
=> hai phân số ở giữa là:\(\frac{10}{15}=\frac{2}{3};\frac{11}{12}\)
a; \(\dfrac{a}{b}\) + \(\dfrac{5}{6}\) = 1 - \(\dfrac{1}{8}\)
\(\dfrac{a}{b}\) + \(\dfrac{5}{6}\) = \(\dfrac{7}{8}\)
\(\dfrac{a}{b}\) = \(\dfrac{7}{8}-\dfrac{5}{6}\)
\(\dfrac{a}{b}=\) \(\dfrac{21}{24}\) - \(\dfrac{20}{24}\)
\(\dfrac{a}{b}=\dfrac{1}{24}\)
b; \(\dfrac{5}{8}-\dfrac{a}{b}\) = \(\dfrac{1}{4}+\dfrac{1}{6}\)
\(\dfrac{5}{8}-\dfrac{a}{b}\) = \(\dfrac{3}{12}+\dfrac{2}{12}\)
\(\dfrac{5}{8}-\) \(\dfrac{a}{b}\) = \(\dfrac{5}{12}\)
\(\dfrac{a}{b}\) = \(\dfrac{5}{8}-\dfrac{5}{12}\)
\(\dfrac{a}{b}\) = \(\dfrac{15}{24}\) - \(\dfrac{10}{24}\)
\(\dfrac{a}{b}\) = \(\dfrac{5}{24}\)
c; \(\dfrac{5}{6}\) - \(\dfrac{1}{4}\) - \(\dfrac{a}{b}\) = \(\dfrac{1}{2}\)
\(\dfrac{10}{12}-\dfrac{3}{12}\) - \(\dfrac{a}{b}\) = \(\dfrac{1}{2}\)
\(\dfrac{7}{12}\) - \(\dfrac{a}{b}\) = \(\dfrac{1}{2}\)
\(\dfrac{a}{b}\) = \(\dfrac{7}{12}\) - \(\dfrac{1}{2}\)
\(\dfrac{a}{b}\) = \(\dfrac{7}{12}-\dfrac{6}{12}\)
\(\dfrac{a}{b}=\dfrac{1}{12}\)
a, \(\dfrac{a}{b}=\dfrac{4}{7}+\dfrac{1}{2}=\dfrac{8+7}{14}=\dfrac{15}{14}\)
b, \(\dfrac{a}{b}=\dfrac{5}{6}+\dfrac{1}{4}+\dfrac{1}{3}=\dfrac{10+3+4}{12}=\dfrac{17}{12}\)
\(a:\dfrac{a}{b}-\dfrac{1}{2}=\dfrac{4}{7}\\ \dfrac{a}{b}=\dfrac{4}{7}+\dfrac{1}{2}\\ \dfrac{a}{b}=\dfrac{8}{14}+\dfrac{7}{14}\\ \dfrac{a}{b}=\dfrac{15}{14}\\ b:\dfrac{a}{b}-\dfrac{1}{4}-\dfrac{1}{3}=\dfrac{5}{6}\\ \dfrac{a}{b}-\left(\dfrac{1}{4}+\dfrac{1}{3}\right)=\dfrac{5}{6}\\ \dfrac{a}{b}-\dfrac{7}{12}=\dfrac{5}{6}\\ \dfrac{a}{b}=\dfrac{5}{6}+\dfrac{7}{12}\\ \dfrac{a}{b}=\dfrac{17}{12}\)