0\; \; ,\; \; x_{1,2}=\frac{13\pm \sqrt{173}}{2}\\\\x^2-13x-1=(x-\frac{13-\sqrt{173}}{2})(x-\frac{13+\sqrt{173}}{2})\\\\\\2)\; \; -7x^2+14x-54=0\; \; ,\; \; 7x^2-14x+54=0\; \; ,\; \; D/4=-329<0\\\\nelzya\; razlozit\\\\3)\; \; 9x^2+x-1=0\; \; ,\; \; D=37>0\; ,\; \; x_{1,2}=\dfrac{-1\pm \sqrt{37}}{2}\\\\9x^2+x-1=9\cdot (x-\frac{-1-\sqrt{37}}{2})(x-\frac{-1+\sqrt{37}}{2})\\\\\\4)\; \; 7x^2+28=0\; \; \to \; \; \; 7x^2=-28\; \; neverno\; ,\; tak\; kak\; \; 7x^2\geq 0" alt="1)\; \; x^2-13x-1=0\; \; ,\; \; D=173>0\; \; ,\; \; x_{1,2}=\frac{13\pm \sqrt{173}}{2}\\\\x^2-13x-1=(x-\frac{13-\sqrt{173}}{2})(x-\frac{13+\sqrt{173}}{2})\\\\\\2)\; \; -7x^2+14x-54=0\; \; ,\; \; 7x^2-14x+54=0\; \; ,\; \; D/4=-329<0\\\\nelzya\; razlozit\\\\3)\; \; 9x^2+x-1=0\; \; ,\; \; D=37>0\; ,\; \; x_{1,2}=\dfrac{-1\pm \sqrt{37}}{2}\\\\9x^2+x-1=9\cdot (x-\frac{-1-\sqrt{37}}{2})(x-\frac{-1+\sqrt{37}}{2})\\\\\\4)\; \; 7x^2+28=0\; \; \to \; \; \; 7x^2=-28\; \; neverno\; ,\; tak\; kak\; \; 7x^2\geq 0" align="absmiddle" class="latex-formula">
получили полный квадрат