The line of symmetry of the parabola whose equation is y = ax2 - 4x + 3 is x = -2. what is the value of "a"?

For equation
  y = ax² +bx +c
the line of symmetry is given by
  x = -b/(2a)

Filling in the given values, we have
  -2 = -(-4)/(2a)
  a = 4/(2(-2)) = -1

The value of "a" is -1.