f（x）=sin（πx/4-π/6）-2cos²πx/8+1
={sinπx/4*cosπ/6-cosπx/4*sinπ/6}-{2cos²πx/8-1}
={sinπx/4*cosπ/6-cosπx/4*sinπ/6}-{cos²πx/8-sin²πx/8}
={sinπx/4*cosπ/6-cosπx/4*sinπ/6}-cosπx/4
=√3/2sinπx/4-3/2cosπx/4