Giải các bất phương trình mũ sau :
a) \(\left(8,4\right)^{\dfrac{x-3}{x^2+1}}< 1\)
b) \(2^{\left|x-2\right|}\ge4^{\left|x+1\right|}\)
c) \(\dfrac{4^x-2^{x+1}+8}{2^{1-x}}< 8^x\)
d) \(\dfrac{1}{3^x+5}\le\dfrac{1}{3^{x+1}-1}\)
Giải các bất phương trình lôgarit sau :
a) \(\dfrac{\ln x+2}{\ln x-1}< 0\)
b) \(\log^2_{0,2}x-\log_{0,2}x-6\le0\)
c) \(\log\left(x^2-x-2\right)< 2\log\left(3-x\right)\)
d) \(\ln\left|x-2\right|+\ln\left|x+4\right|\le3\ln2\)
Giải các bất phương trình sau :
a) \(\left(2x-7\right)\ln\left(x+1\right)>0\)
b) \(\left(x-5\right)\left(\log x+1\right)< 0\)
c) \(2\log^3_2x+5\log^2_2x+\log_2x-2\ge0\)
d) \(\ln\left(3e^x-2\right)\le2x\)
Tìm số tự nhiên n bé nhất sau cho :
a) \(\left(\dfrac{1}{2}\right)^n\le10^{-9}\)
b) \(3-\left(\dfrac{7}{5}\right)^n\le0\)
c) \(1-\left(\dfrac{4}{5}\right)^n\ge0,97\)
d) \(\left(1+\dfrac{5}{100}\right)^n\ge2\)
a) \(\left(\dfrac{1}{2}\right)^n\le10^{-9}\)\(\Leftrightarrow2^{-n}\le10^{-9}\)\(\Leftrightarrow-n\le log^{10^{-9}}_2\)\(\Leftrightarrow-n\le-9log^{10}_2\)\(\Leftrightarrow n\ge9log^{10}_2\)\(\Leftrightarrow n\ge30\).
Vậy \(n=30\).
b) \(3-\left(\dfrac{7}{5}\right)^n\le0\)
\(\Leftrightarrow-\left(\dfrac{7}{5}\right)^n\le-3\)
\(\Leftrightarrow\left(\dfrac{7}{5}\right)^n\ge3\)\(\Leftrightarrow n\ge log^3_{\dfrac{7}{5}}\)
\(\Rightarrow\)\(n\in\left\{4;5;6;7;...\right\}\Rightarrow n=4\)
c) \(1-\left(\dfrac{4}{5}\right)^n\ge0,97\)
\(\Leftrightarrow-\left(\dfrac{4}{5}\right)^n\ge-0,3\)
\(\Leftrightarrow\left(\dfrac{4}{5}\right)^n\le0,3\)\(\Leftrightarrow n\ge log^{0,3}_{\dfrac{4}{5}}\)
\(\Rightarrow n\in\left\{6;7;8;9...\right\}\Rightarrow n=6\)
d)\(\left(1+\dfrac{5}{100}\right)^n\ge2\)
\(\Leftrightarrow1,05^n\ge2\)
\(\Rightarrow n\in\left\{15;16;17;18;...\right\}\Rightarrow n=15\)
Trả lời bởi Mới vô
Trả lời bởi Nguyen Thuy Hoa