I have this vector Fe and i would like to graph it to its corresponding xy coordinates. I know that the $i_y$ component is negative, and there is no $i_x$ component.

$\vec{F_e} = F_x\vec{i_x} + F_y\vec{i_y}$

$\vec{F_e} = F_y\vec{(-i_y)}$

And to get there we have:

$F_{ex}=|\vec{F_{ex}}|cos(270)$

$F_{ex}=|\vec{F_{ex}}|sin(270)$

My question is when do we use the sin and when the cos to find its magnitude. Intuitively cos(270) is 0 and sin(270) is -1. But why didn't we set $F_{ex}$ with sin(270). I know the angle between the x axis and the vector is 270.