Brownian motion - one dimensional

[PERAV]

Hi all.

How do i show that $\displaystyle \, x_t\, =\, 2\, \int_0^t z_u\, dz_u\,$ if i know that the one-dimensional Brownian motion is defined by z=(zt) and the process is $\displaystyle \, x\, =\, (x_t)\,$ and is defined by $\displaystyle \, x_t\, =\, {z_t}^2\, -\, t\, ?$

I'm a little lost but I think I have to use Ito's formula.