\(-\dfrac{1}{2}=\dfrac{-1\times5}{2\times5}=-\dfrac{5}{10}\\ -\dfrac{1}{3}=\dfrac{-1\times5}{3\times5}=-\dfrac{5}{15}\\ -\dfrac{5}{10}>-\dfrac{5}{11};-\dfrac{5}{12};-\dfrac{5}{13};-\dfrac{5}{14}>-\dfrac{5}{15}\\ \Rightarrow a\in\left\{-\dfrac{5}{11};-\dfrac{5}{12};-\dfrac{5}{13};-\dfrac{5}{14}\right\}\)

-12 : (\(\dfrac{3}{4}\) - \(\dfrac{5}{6}\))²

= -12 : (-\(\dfrac{1}{12}\))²

= - 12³

= - 1728 

a) \(\left|x\right|-15=6\Rightarrow\left|x\right|=21\Rightarrow\left[{}\begin{matrix}x=21\\x=-21\end{matrix}\right.\)

b) \(\left|x\right|+4=0\Rightarrow\left|x\right|=-4\Rightarrow x\in\varnothing\)

c) \(x^2-16=0\Rightarrow x^2=16=4^2\Rightarrow\left[{}\begin{matrix}x=4\\x=-4\end{matrix}\right.\)

a, /x/-15=6
    /x/     =6+15
   /x/      =21
   x        =\(\pm\)21
b, /x/+4=0

    /x/    =0-4
    /x/    =-4

    x      =4

c, x^2-16=0
   x^2       =0+16

   x^2       =16
   x^2        = (\(\pm\)4)^2
   x            =\(\pm\) 4

Chiều cao của mực nước là:

2,4 : 2 : 1,5 = 0,8 (m)

Kết luận:... 

\(\left(3x+2\right)\left(2x+9\right)-\left(x+2\right)\left(6x+1\right)=\left(x-1\right)-\left(x-6\right)\\ \Leftrightarrow6x^2+31x+18-6x^2-13x-2=x-1-x+6\\ \Leftrightarrow18x+16=5\\ \Leftrightarrow18x=-11\\ \Leftrightarrow x=-\dfrac{11}{18}\)

\(\dfrac{1}{4}+\dfrac{8}{9}\le\dfrac{x}{36}\le1-\left(\dfrac{3}{8}-\dfrac{5}{6}\right)\\ \Rightarrow\dfrac{41}{36}\le\dfrac{x}{36}\le\dfrac{35}{24}\\ \Rightarrow\dfrac{82}{72}\le\dfrac{2x}{72}\le\dfrac{105}{72}\\ \Rightarrow41\le x< 51,5\)

\(\dfrac{1}{4}+\dfrac{8}{9}\le\dfrac{x}{36}< 1-\left(\dfrac{3}{8}-\dfrac{5}{6}\right)\)

\(\Rightarrow\dfrac{41}{36}\le\dfrac{x}{36}< 1-\left(-\dfrac{11}{24}\right)\)

\(\Rightarrow\dfrac{41}{36}\le\dfrac{x}{36}< 1+\dfrac{11}{24}\)

\(\Rightarrow\dfrac{41}{36}\le\dfrac{x}{36}< \dfrac{35}{24}\)

\(\Rightarrow\dfrac{82}{72}\le\dfrac{2x}{72}< \dfrac{105}{72}\)

\(\Rightarrow82\le2x< 105\)

\(\Rightarrow41\le x< \dfrac{105}{2}\)

\(\dfrac{1}{4}+\dfrac{8}{9}\le\dfrac{x}{36}< 1-\left(\dfrac{3}{8}-\dfrac{5}{6}\right)\)

\(\dfrac{\Leftrightarrow41}{36}\le\dfrac{x}{36}< \dfrac{35}{24}\)

\(\dfrac{\Leftrightarrow82}{72}\le\dfrac{2x}{72}< \dfrac{105}{72}\)

\(\Rightarrow82\le2x< 105\)

\(\Rightarrow x=\left\{41;42;43;44;45;46;47;48;49;50;51;52\right\}\)

\(\widehat{BAM}\) = 180⁰ - 120⁰ = 60⁰

\(\widehat{BAN}\) = 100⁰ - 60⁰ = 40⁰

⇒ N₁ = \(\widehat{BAN}\) = 40⁰( hai góc đồng vị)

\(\sqrt{81}=9\\ \sqrt{\dfrac{25}{64}}=\dfrac{5}{8}\\ \sqrt{\left(-3\right)^2}=3\\ \sqrt{169}=13\\ \sqrt{0,0121}=0,11\\ \sqrt{0,49}=0,7\)