Question

1. Nhân các phân số (chú ý rút gọn nếu có thể)

a) -1/5.1/2

b) -1/8.8/9

c) -3/7.14/15

d) -7/5.15/21

e) (-4).7/24

f) -9/13.5/18

Answer 1

\(a.-\dfrac{1}{5}.\dfrac{1}{2}\)

\(=\dfrac{-1.1}{5.2}\)

\(=\dfrac{-1}{10}.\)

\(b.-\dfrac{1}{8}.\dfrac{8}{9}\)

\(=\dfrac{-1.8}{8.9}\)

\(=\dfrac{-1}{9}.\)

\(c.-\dfrac{3}{7}.\dfrac{14}{15}\)

\(=\dfrac{-3.14}{7.15}\)

\(=\dfrac{-3.7.2}{7.3.5}\)

\(=\dfrac{-2}{5}.\)

\(d.-\dfrac{7}{5}.\dfrac{15}{21}\)

\(=\dfrac{-7.15}{5.21}\)

\(=\dfrac{-7.5.3}{5.7.3}\)

\(=-1.\)

\(e.-4.\dfrac{7}{24}\)

\(=\dfrac{-4.7}{24}\)

\(=\dfrac{-4.7}{4.6}\)

\(=\dfrac{-7}{6}.\)

\(f.-\dfrac{9}{13}.\dfrac{5}{18}\)

\(=\dfrac{-9.5}{13.18}\)

\(=\dfrac{-9.5}{13.9.2}\)

\(=\dfrac{-1.5}{13.2}\)

\(=\dfrac{-5}{26}.\)