Question

Choose the equation below whose axis of symmetry is x = 2.

y = x2 + 4x + 2

y = x2 − 4

y = x2 − 2

y = x2 − 4x + 2

Answer 1

Calculate -b/2a until you find one where the result is 2

Answer 2

The formula for the axis of symmetry is x = -b/2a.

Use y = ax² + bx + c, along with the first-mentioned formula to determine the correct equation.

1) y = x² + 4x + 2

a = 1
b = 4
c = 2

x = -4/(2)
==> -2 [Not what we want!]

2. y = x² - 4

a = 1
b = 0
c = -4

x = -0/2
==> 0 [This doesn't match with x = 2!]

3. Same as equation #2. The axis of symmetry is x = 0.

4. y = x² - 4x + 2

a = 1
b = -4
c = 2

x = -(-4)/(2)
==> 4/2
==> 2 [Yes! That's the equation with the axis of symmetry of x = 2!]

Answer 3

You get it?