x = λ 1 x 1 + λ 2 x 2 + λ 3 x 3 + ( 1 − λ 1 − λ 2 − λ 3 ) x 4 y = λ 1 y 1 + λ 2 y 2 + λ 3 y 3 + ( 1 − λ 1 − λ 2 − λ 3 ) y 4 z = λ 1 z 1 + λ 2 z 2 + λ 3 z 3 + ( 1 − λ 1 − λ 2 − λ 3 ) z 4 {\displaystyle {\begin{matrix}x=\lambda _{1}x_{1}+\lambda _{2}x_{2}+\lambda _{3}x_{3}+(1-\lambda _{1}-\lambda _{2}-\lambda _{3})x_{4}\\y=\lambda _{1}y_{1}+\lambda _{2}y_{2}+\lambda _{3}y_{3}+(1-\lambda _{1}-\lambda _{2}-\lambda _{3})y_{4}\\z=\lambda _{1}z_{1}+\lambda _{2}z_{2}+\lambda _{3}z_{3}+(1-\lambda _{1}-\lambda _{2}-\lambda _{3})z_{4}\\\end{matrix}}}