Answer
$(y-1)^2=-x+2$
Work Step by Step
If the major axis of the parabola is parallel to the y-axis then it is in the form of $4k(y-a)=(x-b)^2$, where $(b,a)$ is the vertex of the parabola and $k$ is a constant (positive if open up, negative if open down).
If the major axis of the parabola is parallel to the x-axis then it is in the form of $4k(x-a)=(y-b)^2$, where $(a,b)$ is the vertex of the parabola and $k$ is a constant. (positive if open right, negative if open left).
Here the major axis is parallel to the x-axis and the vertex is in $(2,1)$.
Thus the equation becomes $(y-1)^2=4k(x-2)$.
We also know that $(1,0)$ is on the graph, hence plugging in $x=1,y=0$ gives us: $(0-1)^2=4k(1-2)\\1=-4k\\k=-\frac{1}{4}$.
Hence our equation: $(y-1)^2=4(-\frac{1}{4})(x-2)\\(y-1)^2=-(x-2)\\(y-1)^2=-x+2$
