â(1+sinθ)-â(1-sinθ)
=â[1+2sin(θ/2)cos(θ/2)]-â[1-2sin(θ/2)cos(θ/2)]
=â[sin²(θ/2)+2sin(θ/2)cos(θ/2)+cos²(θ/2)]-â[sin²(θ/2)-2sin(θ/2)cos(θ/2)+cos²(θ/2)]
=â[sin(θ/2)+cos(θ/2)]²-â[sin(θ/2)-cos(θ/2)]²
=|sin(θ/2)+cos(θ/2)|+|sin(θ/2)-cos(θ/2)|
æ没æç»åºÎ¸çèå´ï¼æçè¯ä¸é¢å¯ä»¥ç»§ç»åç®ä¸å»ã
追é®270·â¤Î¸â¤360·åæå¿äºï¼Sorry.
追ç270°â¤Î¸â¤360°
135°â¤Î¸/2â¤180°
sin(θ/2)+cos(θ/2)â¤0
sin(θ/2)-cos(θ/2)â¥0
æ以|sin(θ/2)+cos(θ/2)|+|sin(θ/2)-cos(θ/2)|
=-sin(θ/2)-cos(θ/2)+sin(θ/2)-cos(θ/2)
=-2cos(θ/2)