\(\Leftrightarrow2\sqrt{x-4}=5\left(x\ge4\right)\\ \Leftrightarrow\sqrt{x-4}=\dfrac{5}{2}\\ \Leftrightarrow x-4=\dfrac{25}{4}\\ \Leftrightarrow x=\dfrac{41}{4}\left(tm\right)\)

\(A=\left(4x-1\right)\left(3x+1\right)-5x\left(x-3\right)-\left(x-4\right)\left(x-3\right)\)

\(=\left(4x-1\right)\left(3x+1\right)-\left(5x+x-4\right)\left(x-3\right)\)

\(=12x^2+4x-3x-1-6x^2+4x+18x-12\)

\(=18x^2+19x-13\)

4. No, there aren't(one theater for opera and ballet)
6. No it isn't (It is the home of .....Australian Ballet....)
 

`@TH1: x < 1`

Ta có: `Bth=1-x+3-x+5-x+7-x=16-4x`

`@TH2: 1 <= x < 3`

Ta có: `Bth=x-1+3-x+5-x+7-x=14-2x`

`@TH3: 3 <= x <= 5`

Ta có: `Bth=x-1+x-3+5-x+7-x=8`

`@TH4: 5 < x <= 7`

Ta có: `Bth=x-1+x-3+x-5+7-x=2x-2`

`@TH5: x > 7`

Ta có: `Bth=x-1+x-3+x-5+x-7=4x-16`

\(\left(x-3\right)\cdot\left(y-5\right)=3\)

=>\(\left(x-3\right)\cdot\left(y-5\right)=1\cdot3=3\cdot1=\left(-1\right)\cdot\left(-3\right)=\left(-3\right)\cdot\left(-1\right)\)

=>\(\left(x-3;y-5\right)\in\left\{\left(1;3\right);\left(3;1\right);\left(-1;-3\right);\left(-3;-1\right)\right\}\)

=>\(\left(x,y\right)\in\left\{\left(4;8\right);\left(6;6\right);\left(2;2\right);\left(0;4\right)\right\}\)

á à láo tự lm đuy:)