If I have a function for example f( x ) = x

^{2}+ x then to obtain f( -x) I just put (-x) in place of the x in f(x)

so I get f( -x) = x

^{2}- x

Am I right so far ?

So f(x) and f(-x) look like different functions but if you put a negative number in f(-x) it flips the -x back to +x so are f(x) and f(-x) are equivalent ?

But if I put sin(x) as the argument I get a totally different function

Thanks