Bài 30: trang 19 sgk Toán 6 tập 2
Quy đồng mẫu các phân số sau:
a) \(\frac{11}{120}\) và \(\frac{7}{40}\)
b) \(\frac{24}{146}\) và \(\frac{6}{13}\)
c) \(\frac{7}{30},\frac{13}{60},\frac{-9}{40}\)
d) \(\frac{17}{60},\frac{-5}{18},\frac{-64}{90}\)
Bài Làm:
a) \(BCNN(120;40) = 120\)
\(\frac{11}{120}=\frac{11}{120}\)
\(\frac{7}{40}=\frac{7.3}{40.3}=\frac{21}{120}\)
b) Rút gọn: \({{24} \over {146}} = {{24:2} \over {146:2}} = {{12} \over {73}}\)
\(BCNN(73;13) = 949\)
\({{12} \over {73}}=\frac{12.13}{73.13}=\frac{156}{949}\)
\(\frac{6}{13}=\frac{6.73}{13.73}=\frac{438}{949}\)
c) \(BCNN(30;60;40) = 120\)
\(\frac{7}{30}=\frac{7.4}{30.4}=\frac{28}{120}\)
\(\frac{13}{60}=\frac{13.2}{60.2}=\frac{26}{120}\)
\(\frac{-9}{40}=\frac{-9.3}{40.3}=\frac{-27}{120}\)
d) \(BCNN(60;18;90) = 180\)
\(\frac{17}{60}=\frac{17.3}{60.3}=\frac{51}{180}\)
\(\frac{-5}{18}=\frac{-5.10}{18.10}=\frac{-50}{180}\)
\(\frac{-64}{90}=\frac{-64.2}{90.2}=\frac{-128}{180}\)