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bạn thiếu đề đó mà kết quả là bằng nhau
Mà đây là lớp 4 đó
Ai tích mk mk tích lại cho
Ta có : \(\frac{2009}{987654321}< \frac{2010}{987654321}\)
\(\frac{2010}{24681357}>\frac{2009}{24681357}\)
\(\Rightarrow A=B\)
\(A=\frac{2009}{987654321}+\frac{2010}{246813579}\)
\(=\frac{2009}{987654321}+\frac{2009}{246813579}+\frac{1}{246813579}\)
\(B=\frac{2009}{987654321}+\frac{1}{987654321}+\frac{2009}{246813579}\)
Có \(\frac{1}{246813579}>\frac{1}{987654321}\)
Vậy A > B
Ta có:
\(A=\frac{\frac{1}{2001}+\frac{1}{2002}+...+\frac{1}{4000}}{\frac{1}{1.2}+\frac{1}{3.4}+...+\frac{1}{3999.4000}}\)
\(=\frac{\frac{1}{2001}+\frac{1}{2002}+...+\frac{1}{4000}}{\frac{1}{1}-\frac{1}{2}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{3999}-\frac{1}{4000}}\)
\(=\frac{\frac{1}{2001}+\frac{1}{2002}+...+\frac{1}{4000}}{\left(1+\frac{1}{3}+...+\frac{1}{3999}\right)-\left(\frac{1}{2}+\frac{1}{4}+...+\frac{1}{4000}\right)}\)
\(=\frac{\frac{1}{2001}+\frac{1}{2002}+...+\frac{1}{4000}}{\left(1+\frac{1}{2}+\frac{1}{3}+...+\frac{1}{3999}+\frac{1}{4000}\right)-2.\left(\frac{1}{2}+\frac{1}{4}+...+\frac{1}{4000}\right)}\)
\(=\frac{\frac{1}{2001}+\frac{1}{2002}+...+\frac{1}{4000}}{\left(1+\frac{1}{2}+\frac{1}{3}+...+\frac{1}{3999}+\frac{1}{4000}\right)-\left(1+\frac{1}{2}+...+\frac{1}{2000}\right)}\)
\(=\frac{\frac{1}{2001}+\frac{1}{2002}+...+\frac{1}{4000}}{\frac{1}{2001}+\frac{1}{2002}+...+\frac{1}{4000}}=1\)
Ta lại có:
\(B=\frac{\left(17+1\right)\left(\frac{17}{2}+1\right)...\left(\frac{17}{19}+1\right)}{\left(1+\frac{19}{17}\right)\left(1+\frac{19}{16}\right)...\left(1+19\right)}\)
\(=\frac{\frac{18}{1}.\frac{19}{2}.\frac{20}{3}...\frac{36}{19}}{\frac{36}{17}.\frac{35}{16}.\frac{34}{15}...\frac{20}{1}}\)
\(=\frac{1.2.3...36}{1.2.3...36}=1\)
Từ đây ta suy ra được
\(A-B=1-1=0\)
a) \(\frac{3}{8}:\frac{9}{10}=\frac{3}{8}\cdot\frac{10}{9}=\frac{30}{72}=\frac{5}{12}\)
b) \(\frac{4}{9}:\frac{12}{8}=\frac{4}{9}\cdot\frac{8}{12}=\frac{32}{108}=\frac{8}{27}\)
Xin lỗi, bài này mk ko biết tính bằng cách thuận tiện, chỉ biết làm thế này thôi!!
bđt \(\Leftrightarrow\)\(\left(ab+1\right)\left(bc+1\right)\left(ca+1\right)\ge\left(\frac{10}{3}\right)^3abc\) (*)
đặt \(\left(\sqrt{ab};\sqrt{bc};\sqrt{ca}\right)=\left(x;y;z\right)\)\(\Rightarrow\)\(xyz\le\frac{1}{27}\)
(*) \(\Leftrightarrow\)\(\left(x^2+1\right)\left(y^2+1\right)\left(z^2+1\right)\ge\left(\frac{10}{3}\right)^3xyz\)
\(VT\ge\left(xy+1\right)\left(yz+1\right)\left(zx+1\right)\)
Có \(xy+1\ge10\sqrt[10]{\frac{xy}{9^9}}\)
Tương tự với \(yz+1\)\(;\)\(zx+1\)\(\Rightarrow\)\(VT\ge10^3\sqrt[10]{\frac{\left(xyz\right)^2}{9^{27}}}\)
Ta cần CM \(10^3\sqrt[10]{\frac{\left(xyz\right)^2}{9^{27}}}\ge\frac{10^3}{3^3}xyz\) đúng với \(xyz\le\frac{1}{27}\)
Dấu "=" xảy ra khi \(a=b=c=\frac{1}{3}\)
Đặt \(P=\left(a+\frac{1}{b}\right)\left(b+\frac{1}{c}\right)\left(c+\frac{1}{a}\right)\)
Vì a+b+c=1 nên
\(P=\left(a+\frac{1}{b}\right)\left(b+\frac{1}{c}\right)\left(c+\frac{1}{a}\right)=abc+\frac{1}{abc}+\frac{1}{a}+\frac{1}{b}+\frac{1}{c}+1\)
Từ BĐt Cosi cho 3 số dương ta có:
\(\frac{1}{3}=\frac{a+b+c}{3}\ge\sqrt[3]{abc}\Rightarrow abc\le\frac{1}{27}\)
đặt x=abc thì \(0< x\le\frac{1}{27}\)
do đó: \(x+\frac{1}{x}-27-\frac{1}{27}=\frac{\left(27-x\right)\left(1-27x\right)}{27x}\ge0\)
=> \(x+\frac{1}{x}=abc+\frac{1}{abc}\ge27+\frac{1}{27}=\frac{730}{27}\)
Mặt khác: \(\left(a+b+c\right)\left(\frac{1}{a}+\frac{1}{b}+\frac{1}{c}\right)\ge9\Rightarrow\frac{1}{a}+\frac{1}{b}+\frac{1}{c}\ge9\)
Nên \(P\ge\frac{730}{27}+10=\frac{1000}{27}=\left(\frac{10}{3}\right)^3\)
Dấu "=" xảy ra khi a=b=c\(=\frac{1}{3}\)
Quy đồng
A=(2006.246813579+2007.987654321)/(246...
B=(2007.246813579+2006.987654321)/(246...
MS bằng nhau nên ta so sánh tử:
A'=2006.246813579+2007.987654321=2006.... +987654321
=2006.(246813579+987654321)+987654321
B'=2007.246813579+2006.987654321 =2006.246813579+246813579+2006.987654321
=2006.(246813579+987654321)+246813579
987654321>246813579
Nên A'>B'
Hay A>B
a/b+c>a/a+b+c
b/c+a>b/a+b+c
c/a+b>c/a+b+c
===>a/b+c+b/c+a+c/a+b>a/a+b+c+b/a+b+c+c/a+b+c(1)
==>biểu thức này >1