The line of symmetry for the quadratic equation y = ax 2 - 8x - 3 is x = 2. what is the value of "a"?
a) -2
b) -1
c) 2

1.

the line of symmetry is x=2, means that the x coordinate of the vertex is x=2.

the point x=2 is the midpoint of the roots  and . 

so 



Remark: in the x-axis, if c is the midpoint of a and b, then 

2.
since and are roots 

and

3.
equalizing:







in the left side factorize a, in the left side factorize 8:



in the right side use the difference of squares formula:



simplify by 



substitute  with 4:



a=2

C)2