Question 7318
The quadratic equation is your friend here.
a = 2
b = -1
c = -7

Go to it!
{{{(-b +- sqrt(b^2 - 4ac))/2a}}}
At the start, I get 
{{{(1 +- sqrt(1 + 56))/4}}}
Can you finish it? [do the work to get 2.14 and -1.64, or thereabouts]