so sánh
A =14^15+3 / 14^16+3 ; B =14^16+5 / 14^17+5
giúp mk nhé
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Ta có: A=\(\frac{14^{15}+3}{14^{15}+3}\) = 1
B=\(\frac{14^{16}+5}{14^{17}+5}\) < 1 => B<1=A => B<A.
\(A=\dfrac{14^{14}+1}{14^{15}+1}\)
\(\Rightarrow14.A=\dfrac{14^{15}+14}{14^{15}+1}\)
\(\Rightarrow14.A=\dfrac{14^{15}+1}{14^{15}+1}+\dfrac{13}{14^{15}+1}\)
\(\Rightarrow14.A=1+\dfrac{13}{14^{15}+1}\)
\(B=\dfrac{14^{15}+1}{14^{16}+1}\)
\(\Rightarrow14.B=\dfrac{14^{16}+14}{14^{16}+1}\)
\(\Rightarrow14.B=\dfrac{14^{16}+1}{14^{16}+1}+\dfrac{13}{14^{16}+1}\)
\(\Rightarrow14.B=1+\dfrac{13}{14^{16}+1}\)
Nhận xét: \(\dfrac{13}{14^{15}+1}>\dfrac{13}{14^{16}+1}\) (cùng tử, xét mẫu)
\(\Rightarrow A>B\)
Vậy \(A>B\)
\(\dfrac{1}{4444}< 1,\dfrac{3}{7}< 1,\dfrac{9}{5}>1,\dfrac{7}{3}>1,\dfrac{14}{15}< 1,\dfrac{16}{16}=1,\dfrac{14}{11}>1\)
\(\frac{1}{4}< 1\) ; \(\frac{3}{7}< 1\) ; \(\frac{9}{5}>1\)
\(\frac{7}{3}>1\) ; \(\frac{14}{15}< 1\) ; \(\frac{16}{16}=1\) ; \(\frac{14}{11}>1\)
1/4 < 1; 3/7 < 1; 9/5 > 1; 14/15 < 1; 16/16 = 1; 14/11 > 1.
A = 15/14 + 16/15 + 17/16 + 18/17
Ta thấy :
15/14 > 1
16/15 > 1
17/16 > 1
18/17 > 1
=> A > 4
B tương tự
\(14A=\dfrac{14^{16}+42}{14^{16}+3}=1+\dfrac{39}{14^{16}+3}\)
\(14B=\dfrac{14^{17}+70}{14^{17}+5}=1+\dfrac{65}{14^{17}+5}\)
mà \(\dfrac{39}{14^{16}+3}< \dfrac{65}{14^{17}+5}\)
nên 14A<14B
hay A<B