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[tex]x^{2} +8x-9=0\\ \\ a=1;b=8;c=-9\\ \\ \\ x=\frac{-b+-\sqrt{delta} }{2.a} \\ \\ \\ delta=b^{2}-4.a.c\\ \\ delta=8^{2} -4.1.(-9)\\ \\ delta=64+36\\ \\ delta=100\\ \\ \\ x=\frac{-b+-\sqrt{delta} }{2a} \\ \\ x=\frac{-8+-\sqrt{100} }{2} \\ \\ x=\frac{-8+-10}{2} \\ \\ \\ x'=\frac{-8-10}{2} =\frac{-18}{2} =-9\\ \\ \\ x''=\frac{-8+10}{2} =\frac{2}{2} =1[/tex]