1/2+5/14+2/63+3/108+1/156
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Ta có : \(\frac{1}{2}+\frac{5}{14}+\frac{2}{63}+\frac{3}{108}+\frac{1}{156}\)
\(=\frac{1}{1.2}+\frac{5}{2.7}+\frac{2}{7.9}+\frac{3}{9.12}+\frac{1}{12.13}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{12}+\frac{1}{12}-\frac{1}{13}\)
\(=1-\frac{1}{13}=\frac{12}{13}\)
a: 12/21=4/7=8/14
4/56=1/14
b: 12/15=4/5=24/30
6/36=1/6=5/30
15/50=3/10=9/30
c: 63/77=9/11=81/99
60/108=5/9=55/99
-18/27=-2/3=-66/99
d: -26/-156=1/6=7/42
49/-14=-7/2=-147/42
32/112=2/7=12/42
27.75 +25.27 -150
= 27. ( 75+25 ) -150
= 27.100 - 150
= 2700 - 150 = 2550
2, 34.35 -25 .12 + 105
= 1190 - 300 + 105
= 890 + 105 = 995
51.8 + 25.15 - 63
=408 + 375 - 63
= 783 - 63
= 720
4,918 : 9 + 20 . 46 - 132
=102 + 20 . 46 - 132
= 102 + 920 - 132
= 1022 - 132
= 890
A = \(\dfrac{2}{3}\) + \(\dfrac{3}{18}\) + \(\dfrac{1}{42}\) + \(\dfrac{2}{63}\) + \(\dfrac{3}{108}\)
A = \(\dfrac{2}{1\times3}\) + \(\dfrac{3}{3\times6}\) + \(\dfrac{1}{6\times7}\)+ \(\dfrac{2}{7\times9}\) + \(\dfrac{3}{9\times12}\)
A = \(\dfrac{1}{1}\) - \(\dfrac{1}{3}\) + \(\dfrac{1}{3}\) - \(\dfrac{1}{6}\) + \(\dfrac{1}{6}\) - \(\dfrac{1}{7}\) + \(\dfrac{1}{7}\) - \(\dfrac{1}{9}\) + \(\dfrac{1}{9}\) - \(\dfrac{1}{12}\)
A = 1 - \(\dfrac{1}{12}\)
A = \(\dfrac{11}{12}\)
\(\frac{1}{2}+\frac{5}{14}+\frac{2}{63}+\frac{3}{108}+\frac{1}{156}\)\(=\frac{12}{13}\)
TL:
\(\frac{1}{2}+\frac{5}{14}+\frac{2}{63}+\frac{3}{108}+\frac{1}{156}\)
\(=\frac{12}{13}\)