Tìm x
\(9.27\le\left(\frac{1}{3}\right)^x\le27.243\)
Tìm x
\(9.27\le\left(\frac{1}{3}\right)^x\le27.243\)
\(9.27\le\left(\frac{1}{3}\right)^x\le27.243\)
\(243\le\left(\frac{1}{3}\right)^x\le6561\)
đến đây toi tịt ==
à để xem !!! như thế này này :
\(3^5\le\left(\frac{1}{3}\right)^x\le3^8\)
Ta có \(\frac{1}{3}=0,\left(3\right)=\sqrt{3}=3\)( bt là số vô tỉ nx xem đã )
\(\Rightarrow3^5\le3^x\le3^8\)
\(\Rightarrow x=6;7\)
\(9.27\le\left(\frac{1}{3}\right)^x\le27.243\)
\(\Rightarrow3^2.3^3\le\left(\frac{1}{3}\right)^x\le3^3.3^5\)
\(\Rightarrow3^5\le\left(\frac{1}{3}\right)^x\le3^8\)
\(\Rightarrow x\in\left\{-5;-6;-7;-8\right\}\)
Áp dụng BĐT Cô-si để tìm Max
a. \(y=\left(x+3\right)\left(5-x\right),\left(-3\le x\le5\right)\)
b. \(y=x\left(6-x\right)\left(0\le x\le6\right)\)
c. \(y=\left(x+3\right)\left(5-2x\right)\left(-3\le x\le\frac{5}{2}\right)\)
d. \(y=\left(2x+5\right)\left(5-2x\right)\left(-\frac{5}{2}\le x\le5\right)\)
e. \(y=\left(6x+3\right)\left(5-2x\right)\left(-\frac{1}{2}\le x\le\frac{5}{2}\right)\)
f. \(y=\frac{x}{x^2+2},x\ge0\)
g. \(y=\frac{x^2}{\left(x^2+2\right)^3}\)
Từ bđt Cauchy : \(a+b\ge2\sqrt{ab}\) ta suy ra được \(ab\le\frac{\left(a+b\right)^2}{4}\)
Áp dụng vào bài toán của bạn :
a/ \(y=\left(x+3\right)\left(5-x\right)\le\frac{\left(x+3+5-x\right)^2}{4}=...............\)
b/ Tương tự
c/ \(y=\left(x+3\right)\left(5-2x\right)=\frac{1}{2}.\left(2x+6\right)\left(5-2x\right)\le\frac{1}{2}.\frac{\left(2x+6+5-2x\right)^2}{4}=.............\)
d/ Tương tự
e/ \(y=\left(6x+3\right)\left(5-2x\right)=3\left(2x+1\right)\left(5-2x\right)\le3.\frac{\left(2x+1+5-2x\right)^2}{4}=.......\)
f/ Xét \(\frac{1}{y}=\frac{x^2+2}{x}=x+\frac{2}{x}\ge2\sqrt{x.\frac{2}{x}}=2\sqrt{2}\)
Suy ra \(y\le\frac{1}{2\sqrt{2}}\)
..........................
g/ Đặt \(t=x^2\) , \(t>0\) (Vì nếu t = 0 thì y = 0)
\(\frac{1}{y}=\frac{t^3+6t^2+12t+8}{t}=t^2+6t+\frac{8}{t}+12\)
\(=t^2+6t+\frac{8}{3t}+\frac{8}{3t}+\frac{8}{3t}+12\)
\(\ge5.\sqrt[5]{t^2.6t.\left(\frac{8}{3t}\right)^3}+12=.................\)
Từ đó đảo ngược y lại rồi đổi dấu \(\ge\) thành \(\le\)
Tìm các số nguyên x biết:
\(\frac{1}{2}-\left(\frac{1}{3}+\frac{3}{4}\right)\le x\le\frac{1}{24}-\left(\frac{1}{8}-\frac{1}{3}\right)\)
\(\frac{1}{2}-\left(\frac{1}{3}+\frac{3}{4}\right)\le x\le\frac{1}{24}-\left(\frac{1}{8}-\frac{1}{3}\right)\)
\(\Rightarrow\frac{1}{2}-\frac{13}{12}\le x\le\frac{1}{24}-\left(-\frac{5}{24}\right)\)
\(\Rightarrow\frac{6}{12}-\frac{13}{12}\le x\le\frac{1}{4}\)
\(\Rightarrow\frac{-7}{12}\le x\le\frac{3}{12}\)
\(\Rightarrow x\in\left\{-7;-6;-5;...;0;1;2;3\right\}\)
\(\frac{1}{2}-\left(\frac{1}{3}+\frac{3}{4}\right)\le x\le\frac{1}{24}-\left(\frac{1}{8}-\frac{1}{3}\right)\)
\(\Rightarrow\frac{1}{2}-\frac{1}{3}-\frac{3}{4}\le x\le\frac{1}{24}-\frac{1}{8}+\frac{1}{3}\)
\(\Rightarrow\frac{6-4-9}{12}\le x\le\frac{1-3+8}{24}\)
\(\Rightarrow\frac{-7}{12}\le x\le\frac{6}{24}\)
\(\Rightarrow\frac{-7}{12}\le x\le\frac{1}{4}\)
\(\Rightarrow\frac{-7}{12}\le x\le\frac{3}{12}\)
\(\Rightarrow-7\le x\le3\)
\(\Rightarrow x\in\left\{-7;-6;-5;-4;-3;....;2;3\right\}\)
tìm x, biết:
\(4\frac{1}{3}.\left(\frac{1}{6}-\frac{1}{2}\right)\le x\le\frac{2}{3}.\left(\frac{1}{3}-\frac{1}{2}-\frac{3}{4}\right)\)
thiếu dấu ngoặc rồi thánh!
\(4\frac{1}{3}.\left(\frac{1}{6}-\frac{1}{2}\right)\le x\le\frac{2}{3}.\left(\frac{1}{3}-\frac{1}{2}-\frac{3}{4}\right)\)
\(\frac{13}{3}.\frac{-1}{3}\) \(\le x\le\frac{2}{3}.\frac{-11}{12}\)
\(\frac{-13}{9}\) \(\le x\le\) \(\frac{-11}{18}\)
\(\frac{-26}{18}\) \(\le\frac{18x}{18}\le\frac{-11}{18}\)
Suy ra \(-26\le18x\le-11\)
\(\rightarrow x=-1\)
Vậy x = -1
Tìm số nguyên x biết: a) \(-4\frac{3}{5}.2\frac{4}{23}\le x\le-2\frac{3}{5}:1\frac{6}{15}\)
b) \(-4\frac{1}{3}.\left(\frac{1}{2}-\frac{1}{6}\right)\le x\le-\frac{2}{3}\left(\frac{1}{3}-\frac{1}{2}-\frac{3}{4}\right)\)
Tìm số nguyên x biết \(\frac{1}{2}-\left(\frac{1}{3}+\frac{1}{4}\right)\le x\le\frac{1}{24}-\left(\frac{1}{8}-\frac{1}{3}\right)\)
-1/12<x<1/4
Do -1/12>-1
1/4<1
=>-1<-1/12<x<1/4<1(dòng này bỏ viết ra để hiểu thôi)
=>-1<x<1
Do x nguyên=>x=0
Tìm số nguyên x biết \(-4\frac{1}{3}.\left(\frac{1}{2}-\frac{1}{6}\right)\le x\le-\frac{2}{3}.\left(\frac{1}{3}-\frac{1}{2}-\frac{3}{4}\right)\)
-4/1/3.1/3< x < -2/3.-11/12
-1/4/9< x < 11/18
-26/18< x < 11/18
Vậy x={-26/18;-25/18;.............;11/18}
tìm x \(\in\)z
\(-4\frac{1}{3}.\left(\frac{1}{2}-\frac{1}{6}\right)\le x\le\frac{-2}{3}\left(\frac{1}{3}-\frac{1}{2}-\frac{3}{4}\right)\)
Câu hỏi : Tìm số nguyên x biết : \(\left(-\frac{2}{3}-\frac{1}{2}\right):-\frac{1}{4}\le x\le\left(-\frac{5}{6}+\frac{2}{\frac{1}{4}}:-\frac{3}{2}\right).\left(-\frac{7}{\frac{1}{2}}\right)\)
Giúp ik
\(\left(\frac{-2}{3}-\frac{1}{2}\right):\frac{-1}{4}\le x\le\left(\frac{-5}{6}+\frac{2}{\frac{1}{4}}:\frac{-3}{2}\right)\cdot\left(\frac{-7}{\frac{1}{2}}\right)\)
\(taco:\left(\frac{-2}{3}-\frac{1}{2}\right):\frac{-1}{4}=\frac{-7}{6}:\frac{-1}{4}=\frac{14}{3}\)
\(\left(\frac{-5}{6}+\frac{2}{\frac{1}{4}}:\frac{-3}{2}\right)\cdot\left(\frac{-7}{\frac{1}{2}}\right)=\left(\frac{-5}{6}+\frac{-16}{3}\right)\cdot\left(-14\right)=\frac{-37}{6}\cdot\left(-14\right)=\frac{259}{3}\)
TU DO \(=>X=\frac{14}{3};\frac{15}{3};,,,;\frac{259}{3}\)
CHUC BAN HOC TOT :))