tgx=1;
x=arcrtg1+πn; n∈Z;
x=π/4+πn; n∈Z;
0≤π/4+πn≤3π
0≤1/4+n≤3
-1/4≤n≤2 3/4
n=0⇒x=π/4
n=1⇒x=π/4+π=5π/4
n=2⇒x=π/4+2π=9π/4
