Question

Find the vertex and the axis of symmetry for the following functions.

Answer 1

Answer:

b

Step-by-step explanation:

its correct

Answer 2

Step-by-step explanation:

a)

y = 2x³ + 4x

a polynomial of 3rd degree cannot have an axis of symmetry.

it can only have a point of symmetry, like in this case.

(0, 0) is the point of symmetry, because due to the fact there is no squared term, any negative x values create exactly the same values (in absolute values) as their positive counterparts - just negative.

the vertex of a polynomial of 3rd degree is the point where the function changes directions.

that point for x³ is the origin, as it is for x. the factors only stretch the graph, but the vertex stays the same.

only if we had a term like (x+a)³ in the polynomial, this would shift the vertex.

so, the point of symmetry and the vertex are the same :

(0, 0).

b)

y = -x² + 4x - 5

the vertex form of a quadratic function is

f(x) = a(x − h)² + k

with (h, k) is the vertex.

x = h is the axis of symmetry.

we use "complete the square" to get it into that form.

-x² + 4x - 5 = -(x² - 4x + 5) = -(x - 2)² - 1

therefore,

y = -(x - 2)² - 1

h = 2, k = -1

the vertex is (2, -1)

the axis of symmetry is x = 2