the cosecant function is undefined at all integer multiples of pi.
(1/2)x - pi/4 = k(pi) where k is an integer
x - pi/2 = 2k(pi)
x = 2k(pi) + pi/2 = pi(2k + 1/2) = pi[(4k+1)/2]
vertical asymptotes will occur at ...
x = {..., -11pi/2, -7pi/2, -3pi/2, pi/2, 5pi/2, 9pi/2, 13pi/2, ...}