So sánh: \(A=\dfrac{2016^{2016}+1}{2017^{2016}+1}\) và \(B=\dfrac{2016^{2015}+1}{2016^{2016}+1}\)
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Vì 20162016 + 1 < 20162017 + 1
\(\Rightarrow B< \frac{2016^{2016}+1+2015}{2016^{2017}+1+2015}=\frac{2016^{2016}+2016}{2016^{2017}+2016}=\frac{2016\left(2016^{2015}+1\right)}{2016\left(2016^{2016}+1\right)}=\frac{2016^{2015}+1}{2016^{2016}+1}=A\)
Vậy A > B
Giải:
a)Ta có:
C=1957/2007=1957+50-50/2007
=2007-50/2007
=2007/2007-50/2007
=1-50/2007
D=1935/1985=1935+50-50/1985
=1985-50/1985
=1985/1985-50/1985
=1-50/1985
Vì 50/2007<50/1985 nên -50/2007>-50/1985
⇒C>D
b)Ta có:
A=20162016+2/20162016-1
A=20162016-1+3/20162016-1
A=20162016-1/20162016-1+3/20162016-1
A=1+3/20162016-1
Tương tự: B=20162016/20162016-3
B=1+3/20162016-3
Vì 20162016-1>20162016-3 nên 3/20162016-1<3/20162016-3
⇒A<B
Chúc bạn học tốt!
Làm tiếp:
c)Ta có:
M=102018+1/102019+1
10M=10.(102018+1)/202019+1
10M=102019+10/102019+1
10M=102019+1+9/102019+1
10M=102019+1/102019+1 + 9/102019+1
10M=1+9/102019+1
Tương tự:
N=102019+1/102020+1
10N=1+9/102020+1
Vì 9/102019+1>9/102020+1 nên 10M>10N
⇒M>N
Chúc bạn học tốt!
A và B có tử số nguyên dương bằng nhau, mà mẫu số nguyên dương A<B nên A>B( để dễ hiểu thì ví dụ đây: 1/5 bé hơn 1/6)
Làm cách nào cx được à bạn :v mình biết có mỗi 1 cách cho cái số mũ to này :v
Đặt a = 2016, xét hiệu A - B :
\(A-B=\dfrac{a^{2014}+1}{a^{2015}+1}-\dfrac{a^{2016}+1}{a^{2017}+1}=\dfrac{\left(a^{2014}+1\right)\left(a^{2017}+1\right)-\left(a^{2016}+1\right)\left(a^{2015}+1\right)}{\left(a^{2015}+1\right)\left(a^{2017}+1\right)}\)
Xét tử số : \(T=a^{4031}+a^{2014}+a^{2017}+1-\left(a^{4031}+a^{2016}+a^{2015}+1\right)\)
\(=a^{2014}+a^{2017}-a^{2016}-a^{2015}=a^{2014}\left(1+a^3-a^2-a\right)=a^{2014}\left(a+1\right)\left(a-1\right)^2>0\)
\(\Rightarrow A-B>0\Rightarrow A>B\)
\(A=\dfrac{\dfrac{1}{2017}+\dfrac{2}{2016}+\dfrac{3}{2015}+...+\dfrac{2016}{2}+\dfrac{2017}{1}}{\dfrac{1}{2}+\dfrac{1}{3}+...+\dfrac{1}{2016}+\dfrac{1}{2017}+\dfrac{1}{2018}}\)
\(A=\dfrac{\left(\dfrac{1}{2017}+1\right)+\left(\dfrac{2}{2016}+1\right)+\left(\dfrac{3}{2015}+1\right)+...+\left(\dfrac{2016}{2}+1\right)+1}{\dfrac{1}{2}+\dfrac{1}{3}+...+\dfrac{1}{2016}+\dfrac{1}{2017}+\dfrac{1}{2018}}\)
\(A=\dfrac{\dfrac{2018}{2017}+\dfrac{2018}{2016}+\dfrac{2018}{2015}+...+\dfrac{2018}{2}+\dfrac{2018}{2018}}{\dfrac{1}{2}+\dfrac{1}{3}+...+\dfrac{1}{2016}+\dfrac{1}{2017}+\dfrac{1}{2018}}\)
\(A=\dfrac{2018\left(\dfrac{1}{2}+\dfrac{1}{3}+...+\dfrac{1}{2016}+\dfrac{1}{2017}+\dfrac{1}{2018}\right)}{\dfrac{1}{2}+\dfrac{1}{3}+...+\dfrac{1}{2016}+\dfrac{1}{2017}+\dfrac{1}{2018}}=2018\)
\(10A=\dfrac{10^{2015}+2016+9\cdot2016}{10^{2015}+2016}=1+\dfrac{18144}{10^{2015}+2016}\)
\(10B=\dfrac{10^{2016}+9+18144}{10^{2016}+2016}=1+\dfrac{18144}{10^{2016}+2016}\)
mà \(\dfrac{18144}{10^{2015}+2016}>\dfrac{18144}{10^{2016}+2016}\)
nên A>B
TA có :\(\frac{2015.2016-1}{2015.2016}=\frac{2015.2016}{2015.2016}-\frac{1}{2015.2016}=1-\frac{1}{2015.2016}\)
Ta có:\(\frac{2016.2017-1}{2016.2017}=\frac{2016.2017}{2016.2017}-\frac{1}{2016.2017}=1-\frac{1}{2016.2017}\)
Vì \(2015.2016< 2016.2017\)
\(\Rightarrow\frac{1}{2015.2016}>\frac{1}{2016.2017}\)
\(\Rightarrow1-\frac{1}{2015.2016}< 1-\frac{1}{2016.2017}\)
\(\Rightarrow\frac{2015.2016-1}{2015.2016}< \frac{2016.2017-1}{2016.2017}\)
Vậy \(\frac{2015.2016-1}{2015.2016}< \frac{2016.2017-1}{2016.2017}\)
Nếu:
\(\dfrac{a}{b}< 1\Rightarrow\dfrac{a+m}{b+m}< 1\left(m\in N\right)\)
Ta có:
\(x=\dfrac{2016^{2017}+1}{2016^{2016}+1}< 1\)
\(\Rightarrow x< \dfrac{2016^{2017}+1+2015}{2016^{2016}+1+2015}\Rightarrow x< \dfrac{2016^{2017}+2016}{2016^{2016}+2016}\Rightarrow x< \dfrac{2016\left(2016^{2016}+1\right)}{2016\left(2016^{2015}+1\right)}\Rightarrow x< \dfrac{2016^{2016}+1}{2016^{2015}+1}=y\)
\(\Rightarrow x< y\)
A<B bạn à . Mình chỉ phán đoán thui chứ chi tiết mình chịu . Hề Hề
cam on ban