tanα = 1 是 α = 2kπ + π/4 的必要条件因为：(1)tanα = 1 ，α 未必是 2kπ + π/4 ，还可能是 (2k + 1)π + π/4(2) tan(2kπ + π/4) = 1tanα = 1 是 α = kπ + π/4 的充要条件
必要不充分,α=2kπ+3π/4或α=2kπ+π/4，即α=kπ+π/4
