Respuesta :

irspow
The quadratic formula is the result of completing the square for ax^2+bx+c=0 when a,b, and c are unknown values.  This result is:

x=(-b±√(b^2-4ac))/(2a), we have x^2-x-2=0 so

x=(1±√(1+8))/2

x=(1±√9)/2

x=(1±3)/2

x=-1 and 2