[tex]x^2 +14x - 51=0\\ \\\Delta = b^{2}-4ac =14^{2}-4*1*(-51)=196+204=400 \\ \\x_{1}=\frac{-b-\sqrt{\Delta }}{2a} =\frac{-14- \sqrt{400}}{2}=\frac{-14-20}{2}= \frac{-34}{2}=-17\\ \\x_{2}=\frac{-b+\sqrt{\Delta }}{2a} =\frac{-14+ \sqrt{400}}{2}=\frac{-14+20}{2}= \frac{6}{2}=3[/tex]
