1, Why I wasn't told about it before?

2, By whom the money were stolen.

3. Has my letter been read?

giúp chi?!!

Bài 2: 

a: \(\dfrac{-5}{9}+\dfrac{4}{9}=\dfrac{-1}{9}\)

b: \(=\dfrac{5}{17}+\dfrac{-1}{17}\cdot3=\dfrac{5}{17}-\dfrac{3}{17}=\dfrac{2}{17}\)

c: \(=\dfrac{1}{5}\left(\dfrac{4}{7}+\dfrac{3}{7}\right)-\dfrac{1}{5}=\dfrac{1}{5}-\dfrac{1}{5}=0\)

d: =5,17-2,24-5,17+3,24=1

2:

a: Xét tứ giác DIHK có 

\(\widehat{DIH}=\widehat{DKH}=\widehat{IDK}=90^0\)

Do đó: DIHK là hình chữ nhật

Suy ra: DH=KI(1)

Xét ΔDEF vuông tại D có DH là đường cao ứng với cạnh huyền EF

nên \(DH^2=HE\cdot HF\left(2\right)\)

Từ (1) và (2) suy ra \(IK^2=HE\cdot HF\)

. là chia à

\(720\left(20-71\right)-71\left(-720\right)\)

\(=720.20-720.71+71.720\)

\(=720.20\)

\(=14400\)

bằng 14400 nhé bạn 

thanks

1: \(75^3:\left(-25\right)^3=\left(\dfrac{75}{-25}\right)^3=\left(-3\right)^3=-27\)

2: \(\left(-60\right)^2:\left(-5\right)^2=\dfrac{60^2}{5^2}=12^2=144\)

3: \(169^2:\left(-13\right)^2=\dfrac{169^2}{13^2}=\left(\dfrac{169}{13}\right)^2=13^2=169\)

4: \(\left(\dfrac{1}{2}\right)^2:\left(\dfrac{3}{2}\right)^2=\left(\dfrac{1}{2}:\dfrac{3}{2}\right)^2=\left(\dfrac{1}{3}\right)^2=\dfrac{1}{9}\)

5: \(\left(\dfrac{2}{3}\right)^3:\left(\dfrac{8}{27}\right)^3=\left(\dfrac{2}{3}:\dfrac{8}{27}\right)^3=\left(\dfrac{2}{3}\cdot\dfrac{27}{8}\right)^3=\left(\dfrac{9}{4}\right)^3=\dfrac{729}{64}\)

6: \(\left(\dfrac{5}{4}\right)^4:\left(\dfrac{15}{2}\right)^4=\left(\dfrac{5}{4}:\dfrac{15}{2}\right)^4=\left(\dfrac{5}{4}\cdot\dfrac{2}{15}\right)^4=\left(\dfrac{1}{6}\right)^4=\dfrac{1}{1296}\)

7: \(\left(\dfrac{7}{8}\right)^5:\left(\dfrac{21}{16}\right)^5\)

\(=\left(\dfrac{7}{8}:\dfrac{21}{16}\right)^5\)

\(=\left(\dfrac{7}{8}\cdot\dfrac{16}{21}\right)^5=\left(\dfrac{2}{3}\right)^5=\dfrac{32}{243}\)

8: \(\left(\dfrac{5}{6}\right)^4:\left(\dfrac{25}{18}\right)^4=\left(\dfrac{5}{6}:\dfrac{25}{18}\right)^4=\left(\dfrac{5}{6}\cdot\dfrac{18}{25}\right)^4=\left(\dfrac{3}{5}\right)^4=\dfrac{81}{625}\)

9: 

\(\left(-\dfrac{3}{4}\right)^3:\left(\dfrac{9}{8}\right)^3=\left(-\dfrac{3}{4}:\dfrac{9}{8}\right)^3=\left(-\dfrac{3}{4}\cdot\dfrac{8}{9}\right)^3\)

\(=\left(-\dfrac{2}{3}\right)^3=-\dfrac{8}{27}\)

10:

\(\left(\dfrac{9}{10}\right)^6:\left(\dfrac{27}{-20}\right)^6=\left(\dfrac{9}{10}:\dfrac{-27}{20}\right)^6\)

\(=\left(\dfrac{9}{10}\cdot\dfrac{20}{-27}\right)^6=\left(-\dfrac{2}{3}\right)^6=\dfrac{64}{729}\)