Just use the following formula:
[tex]v= (\frac{-b}{2a}, f( \frac{-b}{2a})) [/tex]
In this problem, b=2 and a=1
Substitute the values into the formula.
v=(-(2)/2(1), f(-(2)/2(1)))
v=(-1,f(-1))
v=(-1,(-1)²+2(-1)-8)
v=(-1,(1-2-8))
v=(-1,-9)
Therefore, the vertex is (-1,-9).
However, you only wanted the x-value which is in fact -1.
Therefore, the correct answer is "C. -1."
To use the zeroes, just solve the quadratic and find the mean of the two zeroes.
So,
[tex] m=\frac{x_{1}+x_{2} }{2} [/tex].
Hope this helps!
