x=2kπ+π/2,k∈z
π/2,5π/2,9π/2.(1)
x=2kπ-π/2,k∈z
-π/2,3π/2,7π/2.(2)
由（1）、（2）综合得：-π/2,π/2,3π/2,5π/2,7π/2,9π/2.
即x=kπ+π2,k∈z