Consider the LP Maximize z = CX subject to 1a, I2 X = b, X 0

Consider the LP Maximize z = CX subject to 1a, I2 X =

b, X Ú 0 Define XB as the current basic vector with B as its associated basis and CB as its vector of objective coefficients. Show that if CB is replaced with the new coefficients DB, the values of zj - cj for the basic vector XB will remain equal to zero. What is the significance of this result?