原式＝1\\/2(1－cos40°)＋1\\/2(1＋cos100°）＋sin20°cos50°\r\n\r\n ＝1＋1\\/2(cos100°－cos40°)＋1\\/2(sin70°－sin30°)\r\n\r\n ＝3\\/4－sin70°sin30°＋1\\/2sin70°\r\n\r\n ＝3\\/4
