Use completing the square:
Ex:

Now apply to your problem.
First factor out the '4' in front of the 'x^2' term

Apply completing the square:
Notice the picture below
recall the "inscribed angle theorem"
now... notice your picture, "x" is just the intercepted arc
Answer:
1/4
Step-by-step explanation:
-1/8 + 3/8 = 2/8 = 1/4