## 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 \[-(y-6)=x^2+2x \rightarrow y=6-x^2-2x\]

.