解析,
cos(x+a)=-1=cos(2kπ+π)
即是,a=2kπ+π-x
tana=-√3/3
故,tan(2kπ+π-x)
=-tanx=-√3/3
即是tanx=√3/3
故,x=2kπ+π/6或(2k+1)π+π/6