So sánh \(\frac{10^{50} + 1}{10^{50} - 3} và \frac{10^{50} - 3}{10^{50} + 1} \)
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Ta có:
\(A=\frac{10^{50}+2}{10^{50}-1}=\frac{10^{50}-1+3}{10^{50}-1}=1+\frac{3}{10^{50}-1}\)
\(B=\frac{10^{50}}{10^{50}-3}=\frac{10^{50}-3+3}{10^{50}-3}=1+\frac{3}{10^{50}-3}\)
Vì \(10^{50}-1>10^{50}-3\Rightarrow\frac{3}{10^{50}-1}< \frac{3}{10^{50}-3}\)(2 phân số có cùng tử số, mẫu số của phân số nào lớn hơn thì phân
số đó nhỏ hơn)
\(\Rightarrow1+\frac{3}{10^{50}-1}< 1+\frac{3}{10^{50}-3}\Rightarrow A< B\)
\(A=\frac{10^{50}+2}{10^{50}-1}=\frac{10^{50}-1+3}{10^{50}-1}=1+\frac{3}{10^{50}-1}.\)
\(B=\frac{10^{50}}{10^{50}-3}=\frac{10^{50}-3+3}{10^{50}-3}=1+\frac{3}{10^{50}-3}.\)
Do 1050-1 > 1050-3 ; => \(1+\frac{3}{10^{50}-3}>1+\frac{3}{10^{50}-1}\)
=> B > A
Ta có: \(A=\frac{10^{50}+2}{10^{50}-1}=\frac{10^{50}-1+3}{10^{50}-1}=\frac{10^{50}-1}{10^{50}-1}+\frac{3}{10^{50}-1}=1+\frac{3}{10^{50}-1}\)
\(B=\frac{10^{50}}{10^{50}-3}=\frac{10^{50}-3+3}{10^{50}-3}=\frac{10^{50}-3}{10^{50}-3}+\frac{3}{10^{50}-3}=1+\frac{3}{10^{50}-3}\)
Vì \(\frac{3}{10^{50}-1}< \frac{3}{10^{50}-3}\Rightarrow1+\frac{3}{10^{50}-1}< 1+\frac{3}{10^{50}-3}\Rightarrow A< B\)
Ta thấy \(10^{50}>10^{50}-3\)
\(\Rightarrow B=\frac{10^{50}}{10^{50}-3}>\frac{10^{50}+2}{10^{50}-3+2}=\frac{10^{50}+2}{10^{50}-1}=A\)
Vậy \(A< B\)
\(A=\frac{10^{50}+2}{10^{50}+1}=\frac{2}{1}=2\)
\(B=\frac{10^{50}}{10^{50}-3}=\frac{-1}{3}\)
\(\Rightarrow A>B\)
a)\(10^{20}=\left(10^2\right)^{10}=100^{10}\left(1\right)\)
\(9^{30}=\left(9^3\right)^{10}=729^{10}\left(2\right)\)
Từ (1) và (2) \(\Rightarrow9^{30}>10^{20}\)
b) \(\left(-5\right)^{30}=5^{30}=125^{10}\)
\(\left(-3\right)^{50}=3^{50}=243^{10}\)
\(\Rightarrow\left(-3\right)^{50}>\left(-5\right)^{30}\)
c)\(64^8=\left(2^6\right)^8=2^{48}\)
\(16^{12}=\left(2^4\right)^{12}=2^{48}\)
\(\Rightarrow64^8=16^{12}\)
\(\frac{10^{50}+1}{10^{50}-3}=\frac{\left(10^{50}-3\right)+4}{10^{50}-3}=1+\frac{4}{10^{50}-3}\)
\(\frac{10^{50}+3}{10^{50}-1}=\frac{\left(10^{50}-1\right)+4}{10^{50}-1}=1+\frac{4}{10^{50}-1}\)
Ta so sánh \(\frac{4}{10^{50}-3}với\frac{4}{10^{50}-1}\) . Ta có \(\frac{4}{10^{50}-3}\) > \(\frac{4}{10^{50}-1}\) => 1050+1/1050-3 > 1050+3/1050-1
Ta có :
\(\frac{10^{50}+1}{10^{50}-3}=\frac{10^{50}-3+4}{10^{50}-3}=1+\frac{4}{10^{50}-3}\)
\(\frac{10^{50}+3}{10^{50}-1}=\frac{10^{50}-1+4}{10^{50}-1}=1+\frac{4}{10^{50}-1}\)
Do \(\frac{4}{10^{50}-3}>\frac{4}{10^{50}-1}\)
\(\Rightarrow1+\frac{4}{10^{50}-3}>1+\frac{4}{10^{50}-1}\)
\(\Rightarrow\frac{10^{50}+1}{10^{50}-3}>\frac{10^{50}+3}{10^{50}-1}\)
Chúc bạn học tốt !!!
C1:A = \(\frac{10^{50}+2}{10^{50}-1}=\frac{10^{50}-1+3}{10^{50}-1}=\frac{10^{50}-1}{10^{50}-1}+\frac{3}{10^{50}-1}\)
= \(1+\frac{3}{10^{50}-1}\)
B = \(\frac{10^{50}}{10^{50}-3}=\frac{10^{50}-3+3}{10^{50}-3}=\frac{10^{50}-3}{10^{50}-3}+\frac{3}{10^{50}-3}\)
= \(1+\frac{3}{10^{50}-3}\)
Vì \(\frac{3}{10^{50}-1}< \frac{3}{10^{50}-3}\)=) \(1+\frac{3}{10^{50}-1}< 1+\frac{3}{10^{50}-3}\)=) \(A< B\)
C2: Áp dụng tính chất : Nếu \(\frac{a}{b}>1\)=) \(\frac{a}{b}>\frac{a+m}{b+m}\)
Vì B > 1 =) B > \(\frac{10^{50}+2}{10^{50}-3+2}=\frac{10^{50}+2}{10^{50}-1}=A\)
(=) B > A
Ta có: \(\dfrac{10^{50}-3}{10^{50}+1}\)<\(\dfrac{10^{50}+1}{10^{50}+1}\)<\(\dfrac{10^{50}+1}{10^{50}-3}\)
=>\(\dfrac{10^{50}-3}{10^{50}+1}\)<\(\dfrac{10^{50}+1}{10^{50}-3}\)
vậy (đpcm)