三角函数具有周期性和对称性,也可以有双对称性(对称轴或对称中心至少存在两个).例如:正弦函数y=sinx(x∈R)的对称轴为x =π/2+kπ(k∈Z),对称中心为(kπ,0)(k∈Z),周期为T=2kπ(k∈Z,k≠0);余弦函数y=cosx(x∈R)的对称轴为x=kπ(k∈Z), The trigonometric function has periodicity and symmetry, and can also have double symmetry (at least two symmetry axes or symmetry centers exist.) For example: the symmetry axis of the sine function y=sinx(x∈R) is x =π/2+kπ (k∈Z), the symmetry center is (kπ, 0)(k∈Z), the period is T=2kπ(k∈Z,k≠0); the symmetry axis of the cosine function y=cosx(x∈R) is x =kπ(k∈Z),