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\(A=\left(1-\frac{1}{3}\right)\left(1-\frac{1}{6}\right)..............\left(1-\frac{1}{780}\right)\)
\(A=\frac{2}{3}.\frac{5}{6}.......\frac{779}{780}\)
\(A=\frac{4}{6}.\frac{10}{12}........\frac{1558}{1560}\)
\(A=\frac{1.4.2.5...........38.41}{2.3.3.4..........39.40}\)
\(A=\frac{\left(1.2.......38\right).\left(4.5..........41\right)}{\left(2.3.......39\right).\left(3.4............40\right)}\)
\(A=\frac{41}{39}\)
\(A=\left(1-\frac{1}{3}\right)\left(1-\frac{1}{6}\right).......\left(1-\frac{1}{780}\right)\)
\(=\left(\frac{3}{3}-\frac{1}{3}\right)\left(\frac{6}{6}-\frac{1}{6}\right)..........\left(\frac{780}{780}-\frac{1}{780}\right)\)
\(=\frac{2}{3}.\frac{5}{6}..............\frac{779}{780}\)
sao nữa??
\(76-\left\{2\cdot\left[2\cdot5^2-\left(31-2\cdot3\right)\right]\right\}\)
\(=76-\left\{2\cdot\left[2\cdot25-\left(31-6\right)\right]\right\}\)
\(=75-\left[2\cdot\left(50-25\right)\right]\)
\(=76-\left(2\cdot25\right)\)
\(=76-50\)
\(=26\)
____________________
\(6^2\cdot10:\left\{780:\left[10^3-\left(2\cdot5^3+35\cdot14\right)\right]\right\}\)
\(=36\cdot10:\left\{780:\left[1000-\left(2\cdot125+490\right)\right]\right\}\)
\(=360:\left\{780:\left[1000-\left(250+490\right)\right]\right\}\)
\(=360:\left[780:\left(1000-740\right)\right]\)
\(=360:\left(780:260\right)\)
\(=360:3\)
\(=120\)
a: =76-{2*[2*25-31+6]}
=76-{2*[50-31+6]}
=76-2*25
=76-50=26
b: \(=360:\left\{\dfrac{780}{1000-2\cdot125-490}\right\}\)
\(=360:\dfrac{780}{260}\)
=360/3=120
`(6^10:6^8):{780:[87.5-(125+5.7^2)+13.5]}`
`=6^2:[780:(435-49.5-125+65)]`
`=36:[780:(435-245-125+65)]`
`=36:(780:130)`
`=36:6`
`=6`
62 . 10 : { 780 : [ 103 - ( 2 . 53 + 35 . 14 ) ] }
= 360 : { 780 : [ 1000 - ( 250 + 490 ) ] }
= 360 : { 780 : [ 1000 - 740 ] }
= 360 : { 780 : 260 }
= 360 : 3
= 120.
\(B=\frac{2}{3}.\frac{5}{6}.\frac{9}{10}...\frac{779}{780}\)
\(B=\frac{4}{6}.\frac{10}{12}.\frac{18}{20}...\frac{1558}{1560}\)
\(B=\frac{1.4}{2.3}.\frac{2.5}{3.4}.\frac{3.6}{4.5}...\frac{38.41}{39.40}\)
\(B=\frac{1.2.3...38}{3.4.5...40}.\frac{4.5.6...41}{2.3.4...39}\)
\(B=\frac{2}{39.40}.\frac{40.41}{2.3}\)
\(B=\frac{41}{39.3}=\frac{41}{297}\)
(2\(\hept{\begin{cases}2\\3\end{cases}}^5\))