So sánh A và B:
A=124.($\frac{1}{1.1985}$+$\frac{1}{2.1986}$+ $\frac{1}{3.1987}$+…+$\frac{1}{16.2000}$)
B=$\frac{1}{1.17}$+$\frac{1}{2.18}$+$\frac{1}{3.19}$+…+$\frac{1}{1984.2000}$
Ai nhanh nhất mk sẽ cho 5 sao+cảm ơn + ctrl hay nhất
So sánh A và B: A=124.($\frac{1}{1.1985}$+$\frac{1}{2.1986}$+ $\frac{1}{3.1987}$+…+$\frac{1}{16.2000}$) B=$\frac{1}{1.17}$+$\frac{1}{2.18}$+$\frac{1
By Jasmine
Ta có : `A = 124 . ( 1/(1.1985) + 1/(2.1986) + …. +1/(16.2000) )`
`=124/1984 . ( 1 – 1/1985 + 1/2 – 1/986 +….+ 1/16 – 1/2000 )`
`=1/16 . [ (1+1/2+…+1/16) – ( 1/1985 + 1/1986+ …. + 1/2000 )`
Lại có :`B=1/(1.17) + 1/(2.18) + ….+1/(1984.2000)`
`=1/16 . [ (1 + 1/2 + …. + 1/16 ) + ( 1/17+1/18 +….+1/1984-1/17-1/18-…-1/1984 )-(1/1985 + 1/1986 +…. +1/200 ) ]`
`=1/16.[ ( 1+1/2+…+1/16 ) – (1/1985+1/1986+…+1/2000 ) ]`
`Do 1/16.[ ( 1+1/2+…+1/16 ) – (1/1985+1/1986+…+1/2000 ) ] = 1/16.[ ( 1+1/2+…+1/16 ) – (1/1985+1/1986+…+1/2000 ) ]`
`⇒ A = B`
Vậy , `A = B`
A=124.(1/1.1985+1/2.1986+…+1/16.2000)
=124/1984.{1-1/1985+1/2-1/986+..+1/16-1/2000)
=1/16.[(1+1/2+…+1/16)-(1/1985+1/1986+…+1/2000)]
B=1/1.17+1/2.18+…+1/1984.2000
=1/16[(1+1/2+…+1/16)+(1/17+1/18+..+1/1984-1/17-1/18-…-1/1984)-(1/1985+1/1986+….+1/200)]
=1/16.[(1+1/2+…+1/16)-(1/1985+1/1986+…+1/2000)]
Vậy A=B