If g(x) = tan (5x2), then g ′(x) = ?

Question

I've worked this problem out like four times already and I keep getting a complete different answer..So I think I'm doing it wrong.
I keep getting these..

g'(x)= cosx^2 5tan
g'(x)= 2cosxtan^2

Answer 1

if u = 5x^2, then

g(u) = tan u
dg/du = sec^2(u)
dg/dx = dg/du * du/dx = 10x sec^2(5x^2)