I am replacing θ with A, so don't get confused
[tex]csc^{2} A-4=0[/tex]
[tex]csc^{2} A- 2^{2} =0[/tex]
[tex](cscA+2)(cscA-2)=0[/tex]
Using zero product property:
EITHER
[tex]cscA+2=0[/tex]
[tex]cscA=-2[/tex]
[tex]A = -30[/tex]°
OR
[tex]cscA-2=0[/tex]
[tex]cscA=2[/tex]
[tex]A=30[/tex]°