a) \(5x\left(12x+7\right)-3x\left(20x-5\right)=-100\)
\(\Leftrightarrow60x^2+35x-60x^2+15x=-100\)
\(\Leftrightarrow50x=-100\)
\(\Leftrightarrow x=\dfrac{-100}{50}\)
\(x=-2\)
b) \(0,6x\left(x-0,5\right)-0,3x\left(2x+1,3\right)=0,138\)
\(\Leftrightarrow0,6x^2-0,3x-0,6x^2-0,39x=0,138\)
\(\Leftrightarrow-0,69x=0,138\)
\(\Leftrightarrow x=-\dfrac{0,138}{0,69}\)
\(\Leftrightarrow x=-\dfrac{1}{5}\)
c) \(\left(6x+1\right)\left(2x-3\right)-\left(4x+7\right)\left(3x-5\right)=-2\)
\(\Leftrightarrow12x^2-18x+2x-3-\left(12x^2-20x+21x-35\right)=-2\)
\(\Leftrightarrow12x^2-16x-3-12x^2-x+35=-2\)
\(\Leftrightarrow-17x+32=-2\)
\(\Leftrightarrow-17x=-34\)
\(\Leftrightarrow x=\dfrac{-34}{-17}\)
\(\Leftrightarrow x=2\)
d) \(2x\left(3x-9\right)-6x\left(x-7\right)=3-\left(4x-5\right)\)
\(\Leftrightarrow6x^2-18x-6x^2+42x=3-4x+5\)
\(\Leftrightarrow24x=8-4x\)
\(\Leftrightarrow28x=8\)
\(\Leftrightarrow x=\dfrac{8}{28}\)
\(\Leftrightarrow x=\dfrac{2}{7}\)
