中三數學-----直角坐標幾何 @ 百科全書

標題:

中三數學-----直角坐標幾何

發問:

已知四邊形ABCD的頂點為A(15,20),B(24,6),C(0,0)和D(-5,15). (a)求證ABCD是梯形(這題OK) (b)若只移動B點使ABCD成為平行四邊形,求B點的新坐標

最佳解答:

B)設B的坐標為(x,y) JoinAD同埋BC mid-point of AD=[(15+(-5))/2 ], [(20+15)/2] =(5,35/2) mid-point of BC=(5,35/2) 5=(0+x)/2 x=10 35/2=(y+0)/2 y=35 所以B點的新坐標為(10,35) slope of AB=[(20-35)/(15-10)]=-3 slope of CD=[(0-15)/(0-(-5))]=-3 所以 slope of AB//slope of CD -------(1) slope of AC=[(20-0)/(15-0)]=4/3 slope of BD=[(35-15)/(10-(-5))]=4/3 所以 slope of AC//slope of BD -------(2) 從(1)同(2), 證明ABCD是一個平行四邊形紅字唔駛寫架係證比你睇