Question 111200
{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}} is the solution of the general quadradic equation {{{ax^2+bx+c=0}}}.
:
The discriminant is the expression under the radical, i.e. {{{b^2-4ac}}}.  It is called that because we can use that value to determine the nature of the roots of the equation.  If this value is 0, the roots are real and equal, if the value is positive, the roots are real and unequal, and if the value is less than zero, the roots are complex in the form {{{a+-bi}}} where {{{i=sqrt(-1)}}}.
:
In this case, the value of the discriminant is {{{(8)^2-4*(-2)*5=64+40=104}}}, which is positive.  Therefore the roots are real and unequal.  In visual terms, if you were to graph the trinomial, you would get a parabola that crossed the x-axis in two distinct places.
: