Cho : \(A=\dfrac{10^{2015}-1}{10^{2016}-1}\) ; \(B=\dfrac{10^{2014}+1}{10^{2015}+1}\). So sánh A và B
Tính
\(A=\left(\dfrac{1}{5}+\dfrac{2013}{2014}+\dfrac{2015}{2016}+1\right)\left(\dfrac{2013}{2014}+\dfrac{2015}{2016}+\dfrac{1}{10}\right)-\left(\dfrac{1}{5}+\dfrac{2013}{2014}+\dfrac{2015}{2016}\right)\left(\dfrac{2013}{2014}+\dfrac{2015}{2016}+\dfrac{1}{10}+1\right)\)
Đặt \(\dfrac{1}{5}+\dfrac{2013}{2014}+\dfrac{2015}{2016}=B;\dfrac{2013}{2014}+\dfrac{2015}{2016}+\dfrac{1}{10}=C\)
\(A=\left(B+1\right)\cdot C-B\cdot\left(C+1\right)\)
\(=BC+C-BC-B\)
=C-B
\(=\dfrac{2013}{2014}+\dfrac{2015}{2016}+\dfrac{1}{10}-\dfrac{1}{5}-\dfrac{2013}{2014}-\dfrac{2015}{2016}=-\dfrac{1}{10}\)
\(A=\left(\dfrac{1}{5}+\dfrac{2013}{2014}+\dfrac{2015}{2016}+1\right)\left(\dfrac{2013}{2014}+\dfrac{2015}{2016}+\dfrac{1}{10}\right)-\left(\dfrac{1}{5}+\dfrac{2013}{2014}+\dfrac{2015}{2016}\right)\left(\dfrac{2013}{2014}+\dfrac{2015}{2016}+\dfrac{1}{10}+1\right)\)
tất nhên là bằng 00000000000000000000000000000000000000
So sánh A = \(\dfrac{10^{2014}+2016}{10^{2015}+2016}\) và B = \(\dfrac{10^{2015}+2016}{10^{2016}+2016}\) giúp mình nhanh với
\(10A=\dfrac{10^{2015}+2016+9\cdot2016}{10^{2015}+2016}=1+\dfrac{18144}{10^{2015}+2016}\)
\(10B=\dfrac{10^{2016}+9+18144}{10^{2016}+2016}=1+\dfrac{18144}{10^{2016}+2016}\)
mà \(\dfrac{18144}{10^{2015}+2016}>\dfrac{18144}{10^{2016}+2016}\)
nên A>B
Cho A= 10^2014+1/10^2015+1 và B= 10^2015+1/10^2016+1. So sánh A và B
cho A= 102014 + 1 / 102015+1 và B =102015 + 1 / 102016+1
Ta co :
A.10
=10^2015+10/10^2015+1
=1+9/10^2015+1
B.10
=1+9/10^2016+1
Ta nhận thấy rang :
9/10^2015+1>9/10^2016+1
A.10>B.10
Vay :A>B
Cho A= 10^2017+3/10^2016+3 và B=10^2016+1/10^2015+1
so sánh A và B
cho A=\(\frac{10^{2015}-1}{10^{2016}-1}\)và B=\(\frac{10^{2014}+1}{10^{2015}+1}\). So sánh A và B
\(A=\frac{10^{2015}-1}{10^{2016}^{ }-1}=\frac{10^{2015}}{10^{2016}}=\frac{1}{1},B=\frac{10^{2014}-1}{10^{2015}-1}=\frac{10^{2014}}{10^{2015}}=\frac{1}{1}A=B\Rightarrow\)
So sánh:
a) A = 102016 - 2 / 102017 - 2 và B = 202015 + 1 / 102016 + 1
b) A = 20162017 - 3 / 20162018 - 3 và B = 20162016 + 3 / 20162017 + 3
c) A = 20172016 - 2015 / 20172017 - 2015 và B = 20172015 + 1 / 20172016 + 1
cho A=10^2014+1/10^2015+1 và B=10^2015+1/10^2016+1. So sánh A và B
nhớ ghi luôn cách giải nghen
Ta có: \(10A=10.\left(\frac{10^{2014}+1}{10^{2015}+1}\right)=\frac{10^{2015}+10}{10^{2015}+1}=\frac{10^{2015}+1+9}{10^{2015}+1}=1+\frac{9}{10^{2015}+1}\)
\(10B=10.\left(\frac{10^{2015}+1}{10^{2016}+1}\right)=\frac{10^{2016}+10}{10^{2016}+1}=\frac{10^{2016}+1+9}{10^{2016}+1}=1+\frac{9}{10^{2016}+1}\)
Vì 1 = 1; 9 = 9 ta so sánh mẫu:
Ta có: 102015 < 102016 => 102015+1 < 102016+1
=> \(1+\frac{9}{10^{2015}+1}>1+\frac{9}{10^{2016}+1}\)
=> 10A > 10B
=> A > B.