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a: =6x5/4=30/4=15/2
b: =8x7/12=56/12=14/3
c: =5x8/7=40/7
d: =15x3/5=9
a: =6x5/4=30/4=15/2
b: =8x7/12=56/12=14/3
c: =5x8/7=40/7
d: =15x3/5=9
a: =25/30+12/30=37/30
b: =24/20-15/20=9/20
c: =36/48=3/4
d: =8/17x1/6=8/102=4/51
`6/11+2/5+16/11+19/13+3/5+7/13`
`=(6/11+16/11)+(2/5+3/5)+(19/13+7/13)`
`=22/11+5/5+26/13`
`=2+1+2=5`
\(A=\dfrac{19+\dfrac{18}{2}+\dfrac{17}{3}+\dfrac{16}{4}+...+\dfrac{1}{19}}{\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{4}+...+\dfrac{1}{20}}\)
Biến đổi tử số
\(19+\dfrac{18}{2}+\dfrac{17}{3}+\dfrac{16}{4}+...+\dfrac{1}{19}\)
= 1 + \(\left(1+\dfrac{18}{2}\right)+\left(1+\dfrac{17}{3}\right)+\left(1+\dfrac{16}{4}\right)+...+\left(1+\dfrac{1}{19}\right)\)
= \(\dfrac{20}{20}+\dfrac{20}{2}+\dfrac{20}{3}+...+\dfrac{1}{19}\)
= 20 x \(\left(\dfrac{1}{2}+\dfrac{1}{3}+...+\dfrac{1}{19}+\dfrac{1}{20}\right)\)
Vậy \(A=\dfrac{19+\dfrac{18}{2}+\dfrac{17}{3}+\dfrac{16}{4}+...+\dfrac{1}{19}}{\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{4}+...+\dfrac{1}{20}}\)
= \(\dfrac{20\times\left(\dfrac{1}{2}+\dfrac{1}{3}+...+\dfrac{1}{19}+\dfrac{1}{20}\right)}{\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{4}+...+\dfrac{1}{20}}=20\)
Vậy A = 20
☹ huhu
\(\dfrac{16}{17}-\dfrac{2}{3}=\dfrac{48}{51}-\dfrac{34}{51}=\dfrac{14}{51}\)