Equation of a Curve Rotated About a Point

What is the equation of the curve

\[y=f(x)\]
after rotation about the point
\[(a,b)\]
?
It is
\[2b-y=f(2a-)) \rightarrow y=2b-f(2a-x)\]
.
For example
\[f(x)=x^2+2x\]
when rotated about the point
\[(3,2)\]
becomes
\[y=2 \times 2- ((2 \times 3 -x)^2+2(2 \times 3 -x)=-44+14x-x^2\]
.

rotation of curve about point