NP
0
K
Khách
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NP
1
TT
2
K
5
14 tháng 1 2018
cho bài kham khảo nè :
A=1.2+2.3+3.4+4.5+...+2017.2018
=> 3A=1.2.3+2.3.3+3.4.3+4.5.3+...+2017.2018.3
3A=1.2.3+2.3(4-1)+3.4(5-2)+4.5(6-3)+...+2017.2018.(2019-2016)
3A=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+4.5.6-3.4.5+...+2017.2018.2019-2016.2017.2018
3A=(1.2.3+2.3.4+3.4.5+4.5.6+...+2017.2018.2019)-(1.2.3+2.3.4+3.4.5+...+2016.2017.2018)
=> 3A=2017.2018.2019 => \(A=\frac{2017.2018.2019}{3};B=\frac{2018^3}{3}=\frac{2018.2018.2018}{3}\)
Ta có: 2017.2019=2017(2018-1)=2017.2018+2017<2017.2018+2018=2018(2017+1)=2018.2018
=> 2017.2018.2019<2018.2018.2018
=> A<B
thank nha
TH
14 tháng 1 2018
A=1.2+2.3+3.4+...+2017.2018
3A=1.2.3+2.3.3+3.4.3+...+2017.2018.3
3A=1.2.3+2.3.(4−1)+3.4.(5−2)+...+2017.2018.(2019−2016)
3A=1.2.3+2.3.4−1.2.3+3.4.5−2.3.4+...+2017.2018.2019−2016.2017.2018
⇒3A=2017.2018.2019
⇒A=2017.2018.20193
A=2017.2018.20193;B=201833=2018.2018.20183
A=2739315938;B=2739316611
⇒A<B
H
2
BT
23 tháng 11 2017
A=1.2+2.3+3.4+4.5+...+2017.2018
=> 3A=1.2.3+2.3.3+3.4.3+4.5.3+...+2017.2018.3
3A=1.2.3+2.3(4-1)+3.4(5-2)+4.5(6-3)+...+2017.2018.(2019-2016)
3A=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+4.5.6-3.4.5+...+2017.2018.2019-2016.2017.2018
3A=(1.2.3+2.3.4+3.4.5+4.5.6+...+2017.2018.2019)-(1.2.3+2.3.4+3.4.5+...+2016.2017.2018)
=> 3A=2017.2018.2019 => \(A=\frac{2017.2018.2019}{3}\); \(B=\frac{2018^3}{3}=\frac{2018.2018.2018}{3}\)
Ta có: 2017.2019=2017(2018-1)=2017.2018+2017<2017.2018+2018=2018(2017+1)=2018.2018
=> 2017.2018.2019<2018.2018.2018
=> A<B
16 tháng 11 2018
Bui The Hao lam dung roi
mk cung dang can bai nay
Thanks vi da dang honganh
DN
1
PT
23 tháng 11 2017
\(A=1.2+2.3+3.4+...+2017.2018\)
\(3A=1.2.3+2.3.3+3.4.3+...+2017.2018.3\)
\(3A=1.2.3+2.3.\left(4-1\right)+3.4.\left(5-2\right)+...+2017.2018.\left(2019-2016\right)\)
\(3A=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+...+2017.2018.2019-2016.2017.2018\)
\(\Rightarrow3A=2017.2018.2019\)
\(\Rightarrow A=\dfrac{2017.2018.2019}{3}\)
\(A=\dfrac{2017.2018.2019}{3};B=\dfrac{2018^3}{3}=\dfrac{2018.2018.2018}{3}\)
\(A=2739315938;B=2739316611\)
\(\Rightarrow A< B\)
10 tháng 1 2023
ƯCLN(2^3*3^a;2^b*3^5)=2^2*3^5 nên b=2 và a<=5
BCNN(2^3*3^a;2^2*3^5)=2^3*3^6 nên a=6
TN
10 tháng 4 2016
ta có:\(A=\frac{8^9+12}{8^9+7}=\frac{8^9+7+5}{8^9+7}=\frac{8^9+7}{8^9+7}+\frac{5}{8^9+7}=1+\frac{5}{8^9+7}\)
\(B=\frac{8^{10}+4}{8^{10}-1}=\frac{8^{10}-1+5}{8^{10}-1}=\frac{8^{10}-1}{8^{10}-1}+\frac{5}{8^{10}-1}=1+\frac{5}{8^{10}-1}\)
vì 810-1>89+7
\(\Rightarrow\frac{5}{8^{10}-1}<\frac{5}{8^9+7}\)
\(\Rightarrow1+\frac{5}{8^{10}-1}<1+\frac{5}{8^9+7}\)
=>A<B