Question 118533
The discriminant of a quadratic is the term: 
{{{b^2-4ac}}}
In your case, a=2, and c=8. Just plug these in and solve for b:
{{{b^2-4*2*8=-15}}}
{{{b^2-64=-15}}}
{{{b^2=49}}}
{{{highlight(b=7)}}}
{{{highlight(b=-7)}}}
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Good Luck,
tutor_paul@yahoo.com