\(PT\Leftrightarrow x\times8,7=266,22\Leftrightarrow x=30,6\)

Vậy: ...

\(4,\)

Ta có: \(\left\{{}\begin{matrix}15=5.3\\65=5.13\end{matrix}\right.\)

\(\RightarrowƯCLN\left(15;65\right)=5\)

\(\Rightarrow C\)

\(5,\)

Ta có: \(BCNN\left(11;9\right)=11.9=99\)

\(\Rightarrow B\)

Diện tích khu đất trồng trọt:

\(x\times y=15\times12=180\left(m^2\right)\)

\(=\left(18\dfrac{2}{3}-6\dfrac{2}{3}\right).\dfrac{5}{6}=\dfrac{5}{6}.12=10\)

\(PT\Leftrightarrow3x+120=78\Leftrightarrow3x=-42\Leftrightarrow x=-14\)

Vậy: ...

\(7,\)

\(a,=\left(4\times5\right)\times78=20\times78=1560\)

\(b,=\left(2\times5\right)\times99=10\times99=990\)

\(19,\Leftrightarrow\left(49+56\right):x=7\Leftrightarrow105:x=7\Leftrightarrow x=15\)

Vậy: ...

\(d,=\dfrac{\left(x-2\right)\left(x-1\right)}{\left(x+4\right)\left(x-1\right)}-\dfrac{x\left(x+4\right)}{\left(x+4\right)\left(x-1\right)}=\dfrac{x^2-x-2x+2-x^2-4x}{\left(x+4\right)\left(x-1\right)}=\dfrac{7x-2}{x^2+3x-4}\)

\(e,=\dfrac{\left(5x-1\right)\left(x+3\right)}{\left(x-2\right)\left(x+3\right)}+\dfrac{\left(3x-1\right)\left(x-2\right)}{\left(x-2\right)\left(x+3\right)}=\dfrac{5x^2+15x-x-3+3x^2-6x-x+2}{\left(x-2\right)\left(x+3\right)}=\dfrac{8x^2+7x-1}{x^2+x-6}\)

\(e,=\dfrac{x\left(3x-5\right)}{x\left(x-2\right)^2}-\dfrac{\left(x-3\right)\left(x-2\right)}{x\left(x-2\right)^2}=\dfrac{3x^2-5x-x^2+2x+3x-6}{x\left(x-2\right)^2}=\dfrac{2x^2-6}{x\left(x-2\right)^2}\)

\(a,=56-27-11-28+16=6\)

\(b,=28+19-28-32+57=44\)