1) -x(-2x+1)-2x2=5
\(\Leftrightarrow\) 2x2-x-2x2=5
\(\Leftrightarrow\) -x=5
\(\Leftrightarrow\) x= -5
2) 2x(-x-\(\dfrac{1}{2}\))+2x2=2
\(\Leftrightarrow\) -2x2 - xx + 2x2 = 2
\(\Leftrightarrow\) -x = 2
\(\Leftrightarrow\) x = -2
3) -3x(-4x-1)+6x(4-2x)=0
\(\Leftrightarrow\) 12x2 + 3x + 24x - 12x2 = 0
\(\Leftrightarrow\) 27x = 0
\(\Leftrightarrow\) x = 0
4) 5x(-x+1) - 5(-x2-x)=0
\(\Leftrightarrow\) -5x2 + 5x + 5x2 + 5x = 0
\(\Leftrightarrow\) 10x = 0
\(\Leftrightarrow\) x = 0
5) -\(\dfrac{7}{3}\)x(3x+1) - \(\dfrac{1}{2}\)x(2-14x)=0
\(\Leftrightarrow\) -7x2 - \(\dfrac{7}{3}\)x - \(\dfrac{1}{2}\)x.2(1-7x) = 0
\(\Leftrightarrow\) -7x2 - \(\dfrac{7}{3}\)x - x.(1-7x) = 0
\(\Leftrightarrow\) -7x2 - \(\dfrac{7}{3}\)x - x + 7x2 = 0
\(\Leftrightarrow\) - \(\dfrac{7}{3}\)x - x = 0
\(\Leftrightarrow\) -7x - 3x = 0
\(\Leftrightarrow\) -10x = 0
\(\Leftrightarrow\) x = 0