a: \(\Leftrightarrow\left(x-1\right)^2=81\)

\(\Leftrightarrow\left[{}\begin{matrix}x-1=9\\x-1=-9\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=10\\x=-8\end{matrix}\right.\)

\(A=\dfrac{2}{3}+\dfrac{-1}{3}=\dfrac{1}{3}\\ B=\dfrac{25}{11}\times\dfrac{13}{12}\times\dfrac{-11}{5}=\dfrac{5\times13\times\left(-1\right)}{1\times12\times1}=\dfrac{-65}{12}\\ C=\left(\dfrac{3}{4}-\dfrac{1}{5}\right)\times\left(\dfrac{2}{5}-\dfrac{4}{5}\right)=\dfrac{11}{20}\times\dfrac{-2}{5}=\dfrac{-11}{50}\)

\(B< -1< C< 0< A\\ \Leftrightarrow B< C< A\)

a, Với x = 3 và y = -2 ta có:

\(A=\dfrac{3}{2}+\dfrac{4}{9}.\left(6-\left|3\right|\right)+\left(-2\right)\)

\(A=\dfrac{3}{2}+\dfrac{4}{9}.\left(6-3\right)-2\)

\(A=\dfrac{3}{2}+\dfrac{4}{9}.3-2\)

\(A=\dfrac{3}{2}+\dfrac{4}{3}-2\)

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

 Với x = 3 và y = -3 ta có:
\(B=\left|2.3-1\right|+\left|3.\left(-3\right)+2\right|\)

\(B=\left|5\right|+\left|-7\right|\)

\(B=5+7=12\)

Hoctot ! ko hiểu chỗ nào cứ hỏi cj nhé

E cảm ơn cj

Ta có:\(\dfrac{2x}{3y}=\dfrac{-1}{3}\Rightarrow\dfrac{2x}{-1}=\dfrac{3y}{3}=\dfrac{2x-3y}{-1-3}=\dfrac{7}{-4}\)

\(\Rightarrow-2x=-\dfrac{7}{4}\Leftrightarrow x=\dfrac{7}{8};y=\dfrac{-7}{4}\)

1: =>|1/4x^2+1/45|=1/20

=>1/4x^2+1/45=1/20 hoặc 1/4x^2+1/45=-1/20

=>1/4x^2=1/36

=>x^2=1/36:1/4=1/9

=>x=1/3 hoặc x=-1/3

2: =(x^2-3)(x^2-2x)

=x(x-2)(x^2-3)

Chúc bạn học tốt!

2xyz+4xyz-\(\frac{1}{2}\) xyz

=(2+4-\(\frac{1}{2}\) )(xxxyyyzzz)

=3.5x³ y³z³

a) \(2x=5y\)⇒\(x=\dfrac{5}{2}y\)⇒\(xy=\dfrac{5}{2}y^2\)

Thay \(xy=250\), ta có:

\(250=\dfrac{5}{2}y^2\)

⇒\(y^2=100\)⇒\(y=+-10\)

+) \(y=10\text{⇒}x=250:10=25\)

+) \(y=-10\text{⇒}x=250:-10=-25\)

\(a,2x=5y\Rightarrow\dfrac{x}{5}=\dfrac{y}{2}=k\\ \Rightarrow x=5k;y=2k\\ xy=250\Rightarrow5k\cdot2k=250\Rightarrow k^2=25\Rightarrow\left[{}\begin{matrix}k=5\\k=-5\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=25;y=10\\x=-25;y=-10\end{matrix}\right.\\ b,\dfrac{x}{3}=\dfrac{y}{2}=\dfrac{z}{4}=a\Rightarrow x=3a;y=2a;z=4a\\ xyz=192\Rightarrow24a^3=192\Rightarrow a^3=8\Rightarrow a=2\\ \Rightarrow\left\{{}\begin{matrix}x=6\\y=4\\z=8\end{matrix}\right.\\ c,\Rightarrow\dfrac{x}{5}=\dfrac{y}{2}=\dfrac{z}{-3}=q\Rightarrow x=5q;y=2q;z=-3q\\ xyz=240\Rightarrow-30q^3=240\Rightarrow q^3=-8\Rightarrow q=-2\\ \Rightarrow\left\{{}\begin{matrix}x=-10\\y=-4\\z=6\end{matrix}\right.\)

2:

a: a^2-b^2

b: (a-b)^2

c: 1/2(a^2+b^2)

d: 1/2(a^3+b^3)