− 3 4 ⋅ 12 − 5 : − 25 16 = − 3 4 ⋅ 12 − 5 ⋅ − 16 25 = 9 5 . − 16 25 = − 144 125

12. − 2 3 2 = 12. 4 9 = 12.4 9 = 4.4 3 = 16 3 = 5 1 3

0 , 8 : − 2 4 5 ⋅ − 5 2 2 = 4 5 : − 14 5 . 25 4 = 4 5 . − 5 14 . 25 4 = − 25 14

− 5 7 ⋅ 49 3 : − 7 6 = − 5 7 ⋅ 49 3 ⋅ − 6 7 = 10

\(a.\dfrac{-25}{16}=-\dfrac{5}{12}.\dfrac{15}{4}\\ b.-\dfrac{25}{16}=-\dfrac{4}{5}:\dfrac{64}{125}\)

a) \(\dfrac{-25}{16}=\dfrac{-5}{12}\cdot\dfrac{15}{4}\)

b) \(\dfrac{-4}{5}:\dfrac{64}{125}=-\dfrac{25}{16}\)

− 9 ⋅ 2 3 ⋅ 5 4 : − 7 = − 9. 5 6 . − 1 7 = 15 14

                                                             Giải

a) Ta có : \(\frac{-25}{16}=\frac{-5}{12}.\frac{15}{4}\)

b) Ta có : \(\frac{-25}{16}=\frac{-4}{5}.\frac{64}{125}\)

\(a)\)

\(\frac{-25}{16}=\frac{\left(-5\right).5}{4.4}=\frac{\left(-5\right).5.3}{4.4.3}=\frac{\left(-5\right).15}{12.4}=\frac{\left(-5\right)}{12}.\frac{15}{4}\)

\(b)\)

\(\frac{-25}{16}=\frac{\left(-25\right).4.5}{16.4.5}=\frac{\left(-4\right).25.5}{5.16.4}=\frac{\left(-4\right)}{5}.\frac{125}{64}=\frac{\left(-4\right)}{5}:\frac{64}{125}\)