Cách làm cho bạn:
a) 2x(12x – 5) – 8x(3x – 1) = 30
$\Leftrightarrow$ 24x$^{2}$ - 10x – 24x$^{2}$ + 8x = 30
$\Leftrightarrow$ -2x = 30
$\Leftrightarrow$ x = -15;
b) 3x(3 – 2x) + 6x(x – 1) = 15
$\Leftrightarrow$ 9x – 6x$^{2}$ + 6x$^{2}$ - 6x = 15
$\Leftrightarrow$ 3x = 15
$\Leftrightarrow$ x = 5.
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