sin(4x) = 0 .......4x = kπx1 = kπ/4 = k*π/4cos(2x) = 0 .......2x = kπ + π/2x2 = kπ/2 + π/4 = (2k + 1)*π/4x1 包含了 x2
（A） M 包含于N
