证明当p＝1／2(a＋b＋c）时,三角形面积为S△＝√p(p－a)(p－b)(p－c) S=1/2*absinC =1/2*ab√[1-(cosC)²] 1-(cosC)²=1-[(a²+b²-c²)/(2ab)]² =[(2ab)²-(a²+b²-c²)...