[tex]x^2-4x+3=0\\a=1;b=-4;c=3\\\Delta=b^2-4ac=(-4)^2-4*1*3=16-12=4\\x_{1,2}=\frac{-b\pm \sqrt{\Delta}}{2a}=\frac{-(-4)\pm \sqrt{4}}{2*1}=\frac{4\pm 2}{2}=2\pm1\\ x_1=2+1=3=>x_1=3\\x_2=2-1=1=>x_2=1\\\\x^2+x-12=0\\a=1;b=1;c=-12\\\Delta=b^2-4ac=1^2-4*1(-12)=1+48=49\\x_{1,2}=\frac{-b\pm \sqrt{\Delta}}{2a}=\frac{-1\pm \sqrt{49}}{2*1}=\frac{-1\pm 7}{2}\\x_1=\frac{-1+7}{2}=\frac{6}{2}=3=>x_1=3\\ x_2=\frac{-1-7}{2}=\frac{-8}{2}=-4=>x_2=-4[/tex]
