I have three vectors $v_1, v_2$, and $v_3$, giving the vertices of a triangle. The $z$-coordinates are the same, so the $(x,y)$-coordinates alone give the vertices of an identical triangle in the $xy$-plane. Is there a general way to find the area of this triangle given the vectors?
$$ v_1 = (v_{x1}, v_{y1}, v_{z1}) \\ v_2 = (v_{x2}, v_{y2}, v_{z2}) \\ v_3 = (v_{x3}, v_{y3}, v_{z3}) $$
?