#f(x) = 1/cos x + 1/sin x = (sin x + cos x)/(sin.x.cos x) = 0# ->
#sin x + cos x = sqrt2.sin (x + pi/4) = 0#
#sin (x + pi/4) = 0 -> (x + pi/4) = 0 and (x + pi/4) = pi#
#x + pi/4 = 0 -> x = - pi/4#
#x + pi/4 = pi -> x = pi - pi/4 = 3pi/4#
Check
#x = -pi/4 -> sec (-pi/4) + csc (-pi/4) = 2/(sqrt2) - 2/(sqrt2) = 0#. OK
#x = (3pi)/4 -> sec ((3pi)/4) + csc ((3pi)/4) = -2/(sqrt2) + 2/(sqrt2) = 0#. OK