Show that $\displaystyle \mathbf{R} = \cos{t} (\mathbf{i} - \mathbf{j}) + \sin{t} (\mathbf{i} + \mathbf{j}) + \frac{1}{2}t\mathbf{k}$ is a helix

I'm not sure what I have to show. I've already computed $\displaystyle \mathbf{R}'(t), \mathbf{R}''(t), \mathbf{T}(t)$ and $\displaystyle \kappa$