设πarctanx=t
因为sint=cost
所以t=kπ+π/4
πarctanx=kπ+π/4
arctanx=k+1/4
因为arctan的值域是(-π/2,π/2)
所以k+1/4∈(-π/2,π/2)
k=-1,0,1
x=tan(-3/4),tan(1/4),tan(5/4)