Equation of Curve Reflected in Line y=k
What is the equation of the curve
\[y=f(x)\]
after reflection in the line
\[y=k\]
?
It is
\[-(y-2k)=f(x) \rightarrow y=2k-f(x)\]
.
For example
\[y=x^2+2x\]
when reflected in the line
\[y=3\]
becomes
\[-(y-6)=x^2+2x \rightarrow y=6-x^2-2x\]
.
