(2) 四边形ABOP由直角三角形AOB和三角形POA组成.
前者的面积为S1 = (1/2)*OA*OB = 1*2/2 = 1
后者的面积为S2 = (1/2)*OA*|OA上的高| = (1/2)*1*|a| = |a|/2 = -a/2 (P在第二象限,a
(2) 四边形ABOP由直角三角形AOB和三角形POA组成.
前者的面积为S1 = (1/2)*OA*OB = 1*2/2 = 1
后者的面积为S2 = (1/2)*OA*|OA上的高| = (1/2)*1*|a| = |a|/2 = -a/2 (P在第二象限,a