sin2a-cos4a=sin2a - 1 + 2sin²2asina + cosa =msin²a +cos²a + 2sinacosa =m²1+2sinacosa =m²sin2a = m² -1所以：sin2a-cos4a=sin2a - 1 + 2sin²2a=m²-1 -1 + 2 m^4 + 4m&...