Answer
$(x-1)^2=-(y-2)$
Work Step by Step
1. Use the given graph, the parabola opens down with vertex $(1,2)$, thus we have $(x-1)^2=-4p(y-2)$
2. Use the point $(2,1)$ on the curve, we have $(2-1)^2=-4p(1-2)$ , thus $p=\frac{1}{4}$
3. The equation is $(x-1)^2=-(y-2)$
