# Math Help - mistake?

1. ## mistake?

i am confused by this sentence in my textbook:
when a section of the curve y=f(x) is reflected in Oy, the equation of that part of the curve becomes y=-f(x)
is this correct?
i take it that Oy is the y axis (god knows why), and in that case isn't a reflection in the y axis equal to y=f(-x)?

2. i take it that Oy is the y axis (god knows why)
Hmm well we're taught this way in France
"y" goes up and "x" goes left. O is the origin.
Ox denotes the absciss axis and Oy denotes the ordinate axis.

Originally Posted by furor celtica
i am confused by this sentence in my textbook:
when a section of the curve y=f(x) is reflected in Oy, the equation of that part of the curve becomes y=-f(x)
is this correct?
and in that case isn't a reflection in the y axis equal to y=f(-x)?
A reflection by Ox gives -f(x)
Yes, if g denotes the function of the curve reflected in Oy, we have g(x)=f(-x)

3. so my textbook is wrong?