So sánh A và B biết:
A=\(\dfrac{100^{100}+1}{100^{90}+1}\) và \(\dfrac{100^{99}+1}{100^{89}+1}\)
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A = \(\frac{100^{100}+1}{100^{90}+1}\)
\(\frac{1}{100^{10}}A=\frac{100^{100}+1}{100^{100}+100^{10}}\)
\(\frac{1}{100^{10}}A=\frac{100^{100}+100^{10}-100^{10}+1}{100^{100}+100^{10}}\)
\(\frac{1}{100^{10}}A=1+\frac{-100^{10}+1}{100^{100}+100^{10}}\)
B = \(\frac{100^{99}+1}{100^{89}+1}\)
\(\frac{1}{100^{10}}B=\frac{100^{99}+1}{100^{99}+100^{10}}\)
\(\frac{1}{100^{10}}B=\frac{100^{99}+100^{10}-100^{10}+1}{100^{99}+100^{10}}\)
\(\frac{1}{100^{10}}B=1+\frac{-100^{10}+1}{100^{99}+100^{10}}\)
Vì \(\frac{-100^{10}+1}{100^{100}+100^{10}}< \frac{-100^{10}+1}{100^{99}+10^{10}}\)nên A < B
Bạn tham khảo nhé
Ta có công thức :
\(\frac{a}{b}< \frac{a+c}{b+c}\) \(\left(\frac{a}{b}< 1;a,b,c\inℕ^∗\right)\)
Áp dụng vào ta có :
\(C=\frac{100^{100}+1}{100^{90}+1}< \frac{100^{100}+1+99}{100^{90}+1+99}=\frac{100^{100}+100}{100^{90}+100}=\frac{100\left(100^{99}+1\right)}{100\left(100^{89}+1\right)}=\frac{100^{99}+1}{100^{89}+1}=D\)
Vậy \(C< D\)
àk bạn ơi mk nhầm :
Ta có công thức :
\(\frac{a}{b}< \frac{a+c}{b+c}\)\(\left(\frac{a}{b}< 1;a,b,c\inℕ^∗\right)\)
\(\frac{a}{b}>\frac{a+c}{b+c}\)\(\left(\frac{a}{b}>1;a,b,c\inℕ^∗\right)\)
Áp dụng công thức thứ hai ta có :
\(C=\frac{100^{100}+1}{100^{90}+1}>\frac{100^{100}+1+99}{100^{90}+1+99}=\frac{100^{100}+100}{100^{90}+100}=\frac{100\left(100^{99}+1\right)}{100\left(100^{89}+1\right)}=\frac{100^{99}+1}{100^{89}+1}=D\)
Vậy \(C>D\) ( vầy mới đúng )
Các bạn nhớ giải chi tiết nha và ghi cả công thức cho mình nhé
Ta có:
\(M=\dfrac{100^{100}+1}{100^{99}+1}\)
\(\Rightarrow\dfrac{M}{100}=\dfrac{100^{100}+1}{100\cdot\left(100^{99}+1\right)}\)
\(\Rightarrow\dfrac{M}{100}=\dfrac{100^{100}+1}{100^{100}+100}\)
\(\Rightarrow\dfrac{M}{100}=1-\dfrac{99}{100^{100}+100}\)
\(N=\dfrac{100^{101}+1}{100^{100}+1}\)
\(\Rightarrow\dfrac{N}{100}=\dfrac{100^{101}+1}{100\cdot\left(100^{100}+1\right)}\)
\(\Rightarrow\dfrac{N}{100}=\dfrac{100^{101}+1}{100^{101}+100}\)
\(\Rightarrow\dfrac{N}{100}=1-\dfrac{99}{100^{101}+100}\)
Mà: \(100^{101}>100^{100}\)
\(\Rightarrow100^{101}+100>100^{100}+100\)
\(\Rightarrow\dfrac{99}{100^{101}+100}< \dfrac{99}{100^{100}+100}\)
\(\Rightarrow1-\dfrac{99}{101^{101}+100}< 1-\dfrac{99}{100^{100}+100}\)
\(\Rightarrow\dfrac{N}{100}< \dfrac{M}{100}\)
\(\Rightarrow N< M\)
c: \(100C=\dfrac{100^{100}+100}{100^{100}+1}=1+\dfrac{99}{100^{100}+1}\)
\(100D=\dfrac{100^{101}+100}{100^{101}+1}=1+\dfrac{99}{100^{101}+1}\)
100^100+1<100^101+1
=>\(\dfrac{99}{100^{100}+1}>\dfrac{99}{100^{101}+1}\)
=>100C>100D
=>C>D
b: \(2020E=\dfrac{2020^{2022}+2020}{2020^{2022}+1}=1+\dfrac{2019}{2020^{2022}+1}\)
\(2020F=\dfrac{2020^{2021}+2020}{2020^{2021}+1}=1+\dfrac{2019}{2020^{2021}+1}\)
2020^2022+1>2020^2021+1(Do 2022>2021)
=>\(\dfrac{2019}{2020^{2022}+1}< \dfrac{2019}{2020^{2021}+1}\)
=>2020E<2020F
=>E<F
Ta có:
A = \(\dfrac{100^{100}+1}{100^{90}+1}\)> 1 \(\Rightarrow\) A > \(\dfrac{100^{100}+1+99}{100^{90}+1+99}\) = \(\dfrac{100^{100}+100}{100^{90}+100}\)
\(\Rightarrow\) A > \(\dfrac{100\left(100^{99}+1\right)}{100\left(100^{89}+1\right)}\) = B
Vậy A > B