在直角坐标平面内,作单位圆,再作直线y=x和y=-x,这两条直线和x,y轴把坐标平面分成8个区域,在这些区域上依次标上序号1、2、3、…、7、8(如图1).一、半角、倍角在单位圆内的活用若角α是第一象限的角,则角2α在一、三象限,其终边落在第1与第5区域内,这是因为:2kπα2kπ+2π,k In the Cartesian coordinate plane, for the unit circle, make straight lines y=x and y=-x. These two lines and the x and y axes divide the coordinate plane into 8 regions. On these regions, the serial numbers are numbered 1 and 2, respectively. ,3,...,7,8 (Fig. 1). One, half-width, double-angle in the unit circle. If the use angle α is the angle of the first quadrant, then the angle 2α is in one or three quadrants, and its end edge falls on the first. In regions 1 and 5, this is because: 2kπα2kπ+2π,k