Answer
$(x-1)^2+\frac{y^2}{4}=1$
Work Step by Step
The ellipse has a major axis parallel to the y-axis, hence the equation of the ellipse here has the form $\frac{(x-h)^2}{b^2}+\frac{(y-k)^2}{a^2}=1$, where $a\gt b\gt0$ and $(h,k)$ is the center.
$(h,k)=(1,0)$, $a=2$, $b=1$, hence the equation is: $\frac{(x-1)^2}{1^2}+\frac{(y-0))^2}{2^2}=1\\(x-1)^2+\frac{y^2}{4}=1$
