Question

Use the zeros of the following quadratic to find the x-value of the vertex.

Answer 1

Just use the following formula:
$v= (\frac{-b}{2a}, f( \frac{-b}{2a}))$

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,
$m=\frac{x_{1}+x_{2} }{2}$.


Hope this helps!