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e) \(\left(\dfrac{-1}{3}\right)\cdot\dfrac{5}{7}=\dfrac{\left(-1\right)\cdot5}{3\cdot7}=\dfrac{-5}{21}\)
f) \(\dfrac{2}{7}:\dfrac{3}{4}=\dfrac{2}{7}\cdot\dfrac{4}{3}=\dfrac{8}{21}\)
\(\left(1-\dfrac{1}{2}\right)\cdot\left(1-\dfrac{1}{3}\right)\cdot\left(1-\dfrac{1}{4}\right)\cdot...\cdot\left(1-\dfrac{1}{99}\right)\)
\(=\dfrac{1}{2}\cdot\dfrac{2}{3}\cdot\dfrac{3}{4}\cdot\dfrac{4}{5}\cdot...\cdot\dfrac{97}{98}\cdot\dfrac{98}{99}\)
\(=\dfrac{1\cdot2\cdot3\cdot...\cdot98}{2\cdot3\cdot4\cdot...\cdot99}\)
\(=\dfrac{1}{99}\)
\(=\dfrac{3}{2}.\dfrac{4}{3}.\dfrac{5}{4}.....\dfrac{99}{98}.\dfrac{100}{99}=\dfrac{100}{2}=50\)
\(\dfrac{x-2}{5}=\dfrac{1-x}{6}\\ =>\left(x-2\right)\cdot6=\left(1-x\right)\cdot5\\ =>6x-12=5-5x\\ =>6x+5x=5+12\\ =>11x=17\\ x=\dfrac{17}{11}\)
(2/3×x-1/3)=2/3+1/3
(2/3×x-1/3)=3/3
2/3×x=3/3+1/3
2/3×x=4/3
x=4/3:3/2
x=4/3×2/3
x=8/9
-4 2 + { -54 : [ ( -2 )3 + 7 x ( -2 ) ] }
= -4 2 + { -54 : [ ( -8 ) + 7 x ( -2 ) ] }
= -4 2 + { -54 : 2 }
= -4 2 + ( -27 )
= ( -16 ) + ( -27 )
= -43 Nếu -42 là ( -4 )2 thì = 16 + ( -27 ) = -11 nhé bạn ^^
-11