86,77 lớn hơn hay bé hơn 86,077

....

\(B=\dfrac{2010}{4x+20\sqrt{x}+30}\)

\(B=\dfrac{2010}{\left(2\sqrt{x}\right)^2+2\cdot2\sqrt{x}\cdot5+25+5}\)

\(B=\dfrac{2010}{\left(2\sqrt{x}+5\right)^2+5}\)

Ta có: \(\left(2\sqrt{x}+5\right)^2+5\ge5\)

\(\Rightarrow B=\dfrac{2010}{\left(2\sqrt{x}+5\right)^2+5}\le\dfrac{2010}{5}=402\)

Vậy: \(B_{min}=402\)

bài 1 là câu b

diện tích khu đất đó là

7 x 5 x 1000 = 35000 / cm2\

đổ 35000 cm2 = 35,0 hoặc 35/10

DS

Khoảng cách : `1`

Số số hạng : \(\dfrac{8192-1}{1}+1=8192\)

Tổng dãy là : \(\dfrac{\left(8192+1\right)\cdot8192}{2}=33558528\)

 ta có :

 \(1=2^0\)

\(2=2^1\)

\(4=2^2\)

\(8=2^3\)

...

\(8192=2^{13}\)

=> A = \(2^0+2^1+2^2+2^3+...+2^{13}\)

=> 2A = \(^{ }2^1+2^2+2^3+...+2^{13}+2^{14}\)

=> 2A - A = ( \(^{ }2^1+2^2+2^3+...+2^{13}+2^{14}\) ) - ( \(2^0+2^1+2^2+2^3+...+2^{13}\))

=> A = \(2^{14}-2^0\)= \(2^{14}-1\)=16384 -1 = 16383

\(X\times2+28=X\times6\)

\(X\times6-X\times2=28\)

\(X\times\left(6-2\right)=28\)

\(X\times4=28\)

\(X=28:4\)

\(X=7\)

Vậy: X=7 

\(\dfrac{3}{4}km^2=750000m^2\)

3/4 km²=750000m²

\(\dfrac{49}{28}:\dfrac{5}{4}\times\dfrac{6}{7}\)

\(=\dfrac{49}{28}\times\dfrac{4}{5}\times\dfrac{6}{7}\)

\(=\dfrac{7}{4}\times\dfrac{4}{5}\times\dfrac{6}{7}\)

\(=\dfrac{7\times4\times6}{4\times5\times7}\)

\(=\dfrac{6}{5}\)

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