Question

The line of symmetry for the quadratic equation y = ax^2 + 8x - 3 is x = 4. What is the value of "a"?

Answer 1

a = - 1

Explanation:

given a quadratic in standard form : y = ax² + bx + c : a ≠ 0

Then the x-coordinate of the vertex is

•
`x_(vertex)` = -
`(b)/(2a)`

The line of symmetry passes through the parabola, hence x-coordinate is 4

y = ax² + 8x - 3 is in standard form

with a = a, b = 8 and c = - 3, hence

-
`(8)/(2a)` = 4 ( multiply both sides by 2a

- 8 = 8a ( divide both sides by 8 )

a = - 1