What are the vertex, focus and directrix of y=x2+4x+4?

1 Answer
Jun 29, 2018

Vertex=(2,0)
Its directrix is y=14
it's focus is (2,14)

Explanation:

By completing the square

y=(x+2)24+4

y=(x+2)2

the parabola is opened upwards

If a parabola is opened upwards then its equation will be

yk=4a(xh)2

where (h,k) are it's vertex

it's directrix is y=ka

and its focus is (h,k+a)Where a is positive real number

so applying this for the following equation

y=(x+2)2

4a=1a=14

it's vertex is (2,0)

it's directrix is y=014=14

it's focus is (2,0+14)=(2,14)