Solving Quadratic Equations using Quadratic Formula

   If  $a{x}^2+bx+c$ = 0, then $x$ =  $\frac{\mathrm{-b}\pm \sqrt{b^2-\mathrm{4ac}}}{\mathrm{2a}}$

So, if  $6x^2-39x-21$ = 0, then

     $x$ =  $\frac{-(-39)\pm \sqrt{{(\mathrm{-39})}^2-(4)(6)(-21)}}{(2)(6)}$

or, $x$ =  $\frac{\mathrm{39}\pm \sqrt{1521+504}}{\mathrm{12}}$

or, $x$ =  $\frac{\mathrm{39}\pm \sqrt{2025}}{\mathrm{12}}$

or, $x$ =  $\frac{\mathrm{39}\pm 45}{\mathrm{12}}$

or,  $x$ =  $\frac{84}{12}$ or,  $x$ =  $\frac{-6}{12}$

or,  $x$ =  $7$ or,  $x$ =  $\frac{-1}{2}$