$\text{1)3x(5x²-2x-1)=15x³-6x²-3x}$
$\text{⇒Đáp án C}$
$\text{2)2x(x-5)-x(3+2x)=26}$
$\text{⇔2x²-10x-3x-2x²=26}$
$\text{⇔-13x=26}$
$\text{⇔x=-2}$
$\text{⇒Đáp án A}$
$\text{3)(x-7)(x-5)=x²-5x-7x+35=x²-12x+35}$
$\text{⇒Đáp án A}$
$\text{4)(3x-1)(2x+1)-6x²=0}$
$\text{⇔6x²+3x-2x-1-6x²=0}$
$\text{⇔x-1=0}$
$\text{⇔x=1}$
$\text{⇒Đáp án D}$
$\text{5)(x+5)²=x²+10x+25}$
$\text{⇒Đáp án D}$
$\text{6)(x-y)²=x²-2xy+y²}$
$\text{⇒Đáp án C}$
