M1-help

I dont understand where minus sign come from ?
please explain

part D

North-west has direction vector $-\mathbf{i} + \mathbf{j}$. In particular, the i component is -ve version of the j component and they are equal in magnitude.

Hence, you want PQ to point north-west so you want its i component to be the -ve of the j component.

Ok that makes sense
But still confused that i component is t-1 so how we know that it is + or negative?