Answer
$(\pm 3, 0)$
Work Step by Step
The standard form of the equation of the ellipse when the major axis is horizontal can be expressed as: $\dfrac{(x-h)^2}{a^2}+\dfrac{(y-k)^2}{b^2}=1$ in which $(h,k)$ is the center, $2a$ is the major axis length, and $2b$ is the minor axis length.
The standard form of the equation of the ellipse when the major axis is vertical can be expressed as: $\dfrac{(x-h)^2}{b^2}+\dfrac{(y-k)^2}{a^2}=1$ in which $(h,k)$ is the center, $2a$ is the major axis length, and $2b$ is the minor axis length.
Since the ellipse is horizontal, the distance between the vertices is equal to $2a$:
$c=\sqrt{a^2-b^2}=\sqrt {5^2-4^2}=3$
So, the coordinates of the focus: $(\pm 3, 0)$
