four vectors

[sevs]

A particle of rest mass Mo is at rest in the laboratory when it decays into three identical particles, each of rest mass mo. Two of the particles (1 and 2) have velocities and directions as shown. [1 is 3c/5 at -90degrees, 2 4c/5 at 180degrees]
(a) Calculate the direction and the speed of particle 3.
(b) Find the ratio Mo/mo=

what's a four vector? how would you use one to solve part (a)?

[dextercioby]

With no intentions of going into complicated differential geometry,a four vector is a vector of a four-dimensional vector/linear space.The expression "4vector" is used for vectors (covariant/contravariant) from a flat/curved Minkowski space called "space-time".