1. Tính:
a) [( $\frac{1}{9}$ : $\frac{8}{27}$) : $\frac{-1}{3}$] : $\frac{81}{128}$
b) $\frac{-7}{15}$ . $\frac{-5}{8}$ . $\frac{15}{-7}$ . (-32)
c) $\frac{8}{9}$ – $\frac{1}{72}$ – $\frac{1}{56}$ – $\frac{1}{42}$ – $\frac{1}{30}$ – $\frac{1}{20}$ – $\frac{1}{12}$ – $\frac{1}{6}$ – $\frac{1}{2}$
1. Tính: a) [( $\frac{1}{9}$ : $\frac{8}{27}$) : $\frac{-1}{3}$] : $\frac{81}{128}$ b) $\frac{-7}{15}$ . $\frac{-5}{8}$ . $\frac{15}{-7}$ . (-32
By Hadley
a) `[( 1/9 : 8/27) : (-1)/3 ] : 81/128`
`= (1/9 . 27/8) . (-3) . 128/81`
`= 3/8 . (-3) . 128/81`
`=-9/8 . 128/81`
`=-16/9`
b) `-7/15 . (-5)/8 . (15/-7) . (-32)`
`= [ -7/15 . (15/-7)] . [ (-5/8 . (-32)]`
`= 1 . 20`
`= 20`
c) `8/9 – 1/72 – 1/56 -…- 1/6 – 1/2`
`= -1/2 – 1/6 -… -1/56 – 1/72 + 8/9`
`= – (1/2 + 1/6 + …+ 1/56 + 1/72) + 8/9`
`= – (1/1.2 + 1/2.3 +…+ 1/7.8 + 1/8.9) + 8/9`
`= – ( 1/1 – 1/2 + 1/2 – 1/3+…+ 1/7- 1/8 + 1/8 – 1/9 ) + 8/9`
`= – ( 1 – 1/9) + 8/9`
`= – 8/9 + 8/9`
`=0`
a, `[(1/9:8/27):-1/3]:81/128`
`= [(1/9.(27)/8).3].128/81`
`= [3/8.3].128/81`
`= 9/8.128/81`
`= (16)/9`
b, `(-7)/5.(-5)/8.15/(-7) .(-32)`
`= 7/8.(15)/(-7) .(-32)`
`= (-15)/8.(-32)`
`= 60`
c, `8/9-1/72-1/56-1/42-1/30-1/20-1/12-1/6-1/2`
`= -1/2-1/6-…-1/72+8/9`
`= -(1/(1.2)+1/(2.3)+…+1/(8.9))+8/9`
`= -(1-1/2+1/2-1/4+…+1/8-1/9)+8/9`
`= -(1-1/9)+8/9`
`= (-8)/9+8/9`
`= 0`