Figure 7

Vector (Pi, θi) represented in an arbitrary Cartesian coordinate system with x- and y-axis as its two orthogonal axes and the closed vectorial triangle constructed by three vectors (Pi, θi) (i = 1, 2, 3).
Vector (Pi, θi) represented in an arbitrary Cartesian coordinate system with x- and y-axis as its two orthogonal axes and the closed vectorial triangle constructed by three vectors (Pi, θi) (i = 1, 2, 3).