Answer:
Para o seu idioma você deve ir para brainly.com.br
Step-by-step explanation:
[tex]a) 7x^2-x-1=0\\a=1, \: b=-1, \: c=-1\\\\x_{1,2}=\frac{-(-1)\pm \sqrt{(-1)^2-4(1)(-1)} }{2(1)} \\\\\\ x_{1}=\frac{1-\sqrt{5} }{2}\\\\x_{2}=\frac{1+ \sqrt{5} }{2}\\[/tex]
[tex]b) -x^2+5x-8=0\\\\a=-1, \: b=5, \: c=-8\\\\x_{1,2}=\frac{-(5)\pm \sqrt{(5)^2-4(-1)(-8)} }{2(-1)} \\\\x_{1,2}=\frac{-(5)\pm \sqrt{25-32} }{-2}\\\\ x_{1}=\frac{-5-\sqrt{-7} }{-2}\\\\x_{2}=\frac{5+ \sqrt{-7} }{-2}\\[/tex]
