giáo viên mà

ghê bn

(15 + x)(6 + x) = 136

<=> 90 + 15x + 6x + x² = 136

<=> 90 + 21x + x² = 136

<=> x² + 21x - 46 = 0

<=> x² + 2x - 23x - 46 = 0

<=> x(x + 2) - 23(x + 2) = 0

<=> (x - 23)(x + 2) = 0

<=> \(\left[{}\begin{matrix}x-23=0\\x+2=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=23\\x=-2\end{matrix}\right.\)

bn giỏi thế

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