\(x\left(x-6\right)=7\Leftrightarrow x^2-6x+9=16\Leftrightarrow\left(x-3\right)^2=16\Leftrightarrow\left[{}\begin{matrix}x=-4+3=-1\\x=4+3=7\end{matrix}\right.\)
\(\Delta=\left(-6\right)^2-4\left(-1\right).1=40>0\Rightarrow\left\{{}\begin{matrix}x_1=\frac{-b+\sqrt{\Delta}}{2a}=3+\sqrt{10}\\x_2=\frac{-b-\sqrt{\Delta}}{2a}=3-\sqrt{10}\end{matrix}\right.\)
\(\Delta=25-4.4.2=-7< 0\Rightarrow vonghiem\)
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a) x(x-6) = 7
=> x2 - 6x - 7 = 0
=> (x-7)(x + 1) = 0
vậy x = 7 hoặc x = -1
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