Time management is very much important in IIT JAM. The eduncle test series for IIT JAM Mathematical Statistics helped me a lot in this portion. I am very thankful to the test series I bought from eduncle.
Nilanjan Bhowmick AIR 3, CSIR NET (Earth Science)
Bidyut sinha
see the second picture,I have attached...We are getting zero(0) if x1,x2,x3,x4 not equal to 0.. otherwise non zero...this is property of Dirac Delta