Câu 1:
1/ $-2x(3x+2)=-2x.3x-2x.2=-6x²-4x$
2/ $67,3²+2.67,3.32,7+32,7²=(67,3+32,7)²=100²=10000$
3/ a/ $x²+xy-2x=x(x+y-2)$
b/ $x²-y²-2x+1=(x-1)²-y²=(x-1+y)(x-1-y)$
Bài 3:
1/ $(x+2)(x-3)+6=x(x+5)$
$↔x²-x-6+6=x²+5x$
$↔x²-x-x²-5x=0$
$↔-6x=0$
$↔x=0$
2/ $\dfrac{2x}{x²+xy}+\dfrac{6x}{x²-y²}+\dfrac{3}{y-x}$
$=\dfrac{2x(x-y)}{x(x+y)(x-y)}+\dfrac{6x²}{x(x-y)(x+y)}-\dfrac{3x(x+y)}{x(x+y)(x-y)}$
$=\dfrac{2x²-2xy+6x²-3x²-3xy}{x(x+y)(x-y)}$
$=\dfrac{5x²-5xy}{x(x+y)(x-y)}$
$=\dfrac{5x(x-y)}{x(x+y)(x-y)}$
$=\dfrac{5}{x+y}$
