"Volume de OABC " = 1/6 (vec(a) "," vec(b) "," vec(c)) "avec" vec(a) ((a_x),(a_y),(a_z)) " , " vec(b) ((b_x),(b_y),(b_z)) " , " vec(b) ((c_x),(c_y),(c_z)) (vec(a) "," vec(b) "," vec(c)) = (vec(a) ^^ vec(b)) . vec(c) = det(vec(a) "," vec(b) "," vec(c)) = c_x|(a_y,b_y),(a_z,b_z)| - c_y|(a_x,b_x),(a_z,b_z)| + c_z|(a_x,b_x),(a_y,b_y)|