T=2π/[(2k+1)π/3]=6/(2k+1)
一个区间上值5/4出现不少于4次且不多于8次,看图知
区间长度应小于4T且>=[3/2+arcsin(1/4)]/π]T(arcsin(1/4)表示一个锐角(单位为弧度),它的正弦值为1/4)
3T/2+2[arcsin(1/4)]T/(2π)=[3/2+arcsin(1/4)]/π]T=<1<4T
即[3/2+arcsin(1/4)]/π][6/(2k+1)]={9+6[arcsin(1/4)]/π}/(2k+1)=<1<4*6/(2k+1)=24/(2k+1),
9+0.48(约)=9+6[arcsin(1/4)]/π=<2k+1<24,
4.24(约)=
k=5,6,7,8,9,10,11