(1-x)³ : (- 0,5625) = 0,525 : 0,7

<=> (1-x)³ : (- 0,5625) = 0,75 

<=> (1-x)³ = -27/64

<=> (1-x)³ = -\(\frac{3^3}{4^3}\)

<=> 1 - x = -3/4 

<=> x = 7/4  thuộc tập Q

Có  \(A=\frac{10^{2005}+1}{10^{2006}+1}\) và \(B=\frac{10^{2006}+1}{10^{2007}+1}\)

\(\Rightarrow10A=\frac{10^{2006}+10}{10^{2006}+1}=\frac{10^{2006}+1}{10^{2006}+1}+\frac{9}{10^{2006}+1}=1+\frac{9}{10^{2006}+1}\)

\(\Rightarrow10B=\frac{10^{2007}+10}{10^{2007}+1}=\frac{10^{2007}+1}{10^{2007}+1}+\frac{9}{10^{2007}+1}=1+\frac{9}{10^{2007}+1}\)

Có \(\Rightarrow\frac{9}{10^{2006}+1}>\frac{9}{10^{2007}+1}\Leftrightarrow1+\frac{9}{10^{2006}+1}>1+\frac{9}{10^{2007}+1}\)

\(\Rightarrow10A>10B\Leftrightarrow A>B\)

\(\frac{17-a}{28+a}=\frac{1}{4}\)

\(28+a=4\left(17-a\right)\)

a + 28 = 68 - 4a 

a + 4a = 68 - 28 

5a = 40 

a = 8 

Vậy số tự nhiên cần tìm là 8.

1 A

2B

BẠN CHO MÌNH ĐI

We cannot deny that. Robots will be very useful to us in the future in all aspects. For example, later, dangerous jobs, robots can help us handle them easily. Robots are also our "arm" later. In general, they are very useful. In addition to the positive things, if we abuse robots too much we will encounter negative things, they are very serious! If we let robots do our jobs for us too much, they will gradually become smarter and replace human positions! Use the robot correctly.

To have a green, clean and beautiful world, we should not: throw litter indiscriminately, plant more trees, do not discharge toxic gases into the environment, etc. , pretty.

dịch:để có một thế giới xanh ,sạch , đẹp chúng ta không nên : vứt rác bừa bãi, trồng nhiều cây hơn, không thải khí độc ra môi trường,....Có như vậy chúng ta mới có một thế giới xanh, sạch, đẹp.

CHÚC MAY MẮN

Thanks bạn Bùi Hương Mai!!!!!

a) \(\frac{113}{13}-\frac{24}{7}-\frac{53}{13}=\frac{60}{13}-\frac{24}{7}\)

=\(\frac{420-312}{91}=\frac{108}{91}\)

b) \(\frac{2}{7}.\left(\frac{51}{4}-\frac{31}{4}\right)=\frac{2}{7}.5=\frac{10}{7}\)

c) \(\frac{3}{5}+1-\frac{1}{20}\)= \(\frac{12}{20}+\frac{20}{20}-\frac{1}{20}=\frac{31}{20}\)

sai r cậu

Đặt \(A=\frac{1}{5^2}+\frac{1}{6^2}+\frac{1}{7^2}+...+\frac{1}{2013^2}\)

\(A=\frac{1}{5\cdot5}+\frac{1}{6\cdot6}+\frac{1}{7\cdot7}+...+\frac{1}{2013\cdot2013}\)

Ta có : \(\frac{1}{5\cdot5}< \frac{1}{4\cdot5}\)

\(\frac{1}{6\cdot6}< \frac{1}{5\cdot6}\)

\(\frac{1}{7\cdot7}< \frac{1}{6\cdot7}\)

...

\(\frac{1}{2013\cdot2013}< \frac{1}{2012\cdot2013}\)

=> \(A=\frac{1}{5^2}+\frac{1}{6^2}+\frac{1}{7^2}+..+\frac{1}{2013^2}< \frac{1}{4\cdot5}+\frac{1}{5\cdot6}+\frac{1}{6\cdot7}+...+\frac{1}{2012\cdot2013}\)

=> \(A< \frac{1}{4}-\frac{1}{2013}\)

=> \(A< \frac{2009}{8052}\)

Lại có \(\frac{2009}{8052}< \frac{1}{4}\)

Theo tính chất bắc cầu => \(A< \frac{1}{4}\)( đpcm )

Sai thì mong bạn bỏ qua