tan (u*pi)=sec^2(u)(pi) = pi*sec^2 (pi*x)

i understand how the derivative would be sec^2u times pi, but how does that multiplication give

pi*sec^2pi*x

where did the x come from?

sec^2u times pi[/tex] is equal to [tex]pi*sec^2 (pi*x) ?

PS I tried wrapping this in [tex] but it came up with all kinds of errors for some reason, let me know if its too crappyly written and i'll find a way to re-write it (im out of time at the mo or I'd rewrite it now)