Answer :
cosec(a) = 1/sin(a)
therefore putting a=0 cosec(0) = 1/sin(0)
but sin(0)=0
therefore, cosec(0)=1/0
hence cosec(0) = undefined
therefore putting a=0 cosec(0) = 1/sin(0)
but sin(0)=0
therefore, cosec(0)=1/0
hence cosec(0) = undefined