（1）x=-3,y=4,r=5
sinα=y/r=4/5
cosα=x/r=-3/5
tanα=y/x=-4/3
（2）y=sinx-√3cosχ
=2[sinx*(1/2)-cosx*(√3/2)]
=2[sinxcos(π/3)-cosxsin(π/3)]
=2sin(x-π/3)
当 x-π/3=2kπ+π/2,即 x=2kπ+5π/6,k∈Z,y有最大值2
当 x-π/3=2kπ-π/2,即 x=2kπ-π/6,k∈Z,y有最小值-2