\(rút gọn biểu thức A = 1.2 + 2.3 +3.4+ ...+ 2010.2011\)
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B
1
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18 tháng 3 2015
x^2+1^2+y^2+1^2+x^2-y^2=2
x^2+1+x^2+1=2
2x^2=2-1-1
2x^2=0
x^2=0:2
x^2=0
Mà 0^2=0=>x=0
PA
0
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TQ
0
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NP
8
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TM
15 tháng 3 2015
- 3/10 +3/11 +3/12 +3/13 +3/14 > 3/15 + 3/15 +3/15 +3/15 +3/15 = 15/15 =1
S < 3/10 +3/10 +3/10 + 3/10 + 3/10 = 15/ 10 < 20/10 =2
HT
0
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TV
0
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H
1
TV
1
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NT
19 tháng 4 2018
\(A=\left(\frac{7}{9}+1\right)\left(\frac{7}{20}+1\right)\left(\frac{7}{33}+1\right)..........\left(\frac{7}{2900}+1\right)\)
\(A=\frac{16}{9}.\frac{27}{20}.\frac{40}{33}.......\frac{2907}{2900}\)
\(A=\frac{2.8}{1.9}.\frac{3.9}{2.10}.\frac{4.10}{3.11}......\frac{51.57}{50.58}\)
\(A=\frac{2.3.4.....51}{1.2.3......50}.\frac{8.9.10.......57}{9.10.11........58}\)
\(A=51.\frac{4}{29}\)
\(A=\frac{204}{59}\)
Vậy \(A=\frac{204}{59}\)
a=1.2 + 2.3 +3.4+ ...+ 2010.2011\
3a=1.2.3+2.3.3+3.4.3+......+2010.2011.3
3a=1.2.3+2.3.(4-1)+3.4.(5-1)+............+2010.2011.(2012-2009)
3a=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+....+2010.2011.2012-2009.2010.2011
3a=2010.2011.2012
a=2010.2011.2012:3
a=?
A=2010.2011.2012:3