Bài 3:
a) Các phân số chưa tối giản là: \(\dfrac{12}{33};\dfrac{14}{49};\dfrac{15}{45}\)
b)
Ta có: \(\dfrac{12}{33}=\dfrac{12:3}{33:3}=\dfrac{4}{11}\)
Ta có: \(\dfrac{14}{49}=\dfrac{14:7}{49:7}=\dfrac{2}{7}\)
Ta có: \(\dfrac{15}{45}=\dfrac{15:5}{45:5}=\dfrac{3}{9}\)
Bài 4:
a) \(\dfrac{2}{5}=\dfrac{2\times7}{5\times7}\)\(=\dfrac{14}{35}\)
\(\dfrac{4}{7}=\dfrac{4\times5}{7\times5}=\dfrac{20}{35}\)
b) \(\dfrac{7}{11}=\dfrac{7\times55}{11\times55}=\dfrac{385}{55}\)
\(\dfrac{12}{55}=\dfrac{12\times11}{55\times11}=\dfrac{132}{55}\)
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