Đề bài - bài 69 trang 36 sgk toán 6 tập 2

Đề bài

Nhân các phân số (rút gọn nếu có thể):

a)\(\dfrac{-1}{4}.\dfrac{1}{3}\);

b)\(\dfrac{-2}{5}.\dfrac{5}{-9}\);

c)\(\dfrac{-3}{4}.\dfrac{16}{17}\);

d)\(\dfrac{-8}{3}.\dfrac{15}{24}\);

e)\((-5).\dfrac{8}{15}\);

g)\(\dfrac{-9}{11}.\dfrac{5}{18}\).

Lời giải chi tiết

a)\(\dfrac{-1}{4}.\dfrac{1}{3} = \dfrac{-1.1}{4.3}\) = \(\dfrac{-1}{12}\)

b)\(\dfrac{-2}{5}.\dfrac{5}{-9} = \dfrac{(-2).5}{5.(-9)}\)\(= \dfrac{(-2).1}{1.(-9)}=\dfrac{-2}{-9}= \dfrac{2}{9}\)

c)\(\dfrac{-3}{4}.\dfrac{16}{17} = \dfrac{(-3).16}{4.17} \)\(=\dfrac{(-3).4}{1.17}=\dfrac{-12}{17}\)

d)\(\dfrac{-8}{3}.\dfrac{15}{24} = \dfrac{(-8).15}{3.24} \)\(=\dfrac{(-1).5}{1.3}=\dfrac{-5}{3}\)

e)\((-5).\dfrac{8}{15} = \dfrac{(-5).8}{1.15}\)\(=\dfrac{(-1).8}{1.3}=\dfrac{-8}{3}\)

g)\(\dfrac{-9}{11}.\dfrac{5}{18} = \dfrac{(-9).5}{11.18}\) \(=\dfrac{(-1).5}{11.2}=\dfrac{-5}{22}\)