24.1旋轉(zhuǎn)

（第5課時(shí)）1/11

如圖，是一個(gè)6×6棋盤，兩人各持若干張1×2卡片輪番在棋盤上蓋卡片，每人每次用一張卡片蓋住相鄰兩個(gè)空格，誰找不出相鄰兩個(gè)空格放卡片就算誰輸，你用什么辦法戰(zhàn)勝對(duì)手呢？思索2/11xyo復(fù)習(xí)回顧3/11xyoA(3，0)A1(-3，0)AA1B(0，-2)B1(0，2)C(2，1)C1(-2，-1)在直角坐標(biāo)系中，做出以下已知點(diǎn)關(guān)于原點(diǎn)對(duì)稱點(diǎn)。D(-1，2)D1(1，-2)復(fù)習(xí)回顧4/11

兩個(gè)點(diǎn)關(guān)于原點(diǎn)對(duì)稱時(shí)，它們坐標(biāo)符號(hào)相反，即點(diǎn)P(x,y)關(guān)于原點(diǎn)對(duì)稱點(diǎn)為P1(-x,-y)總結(jié)新知5/11以下各點(diǎn)中哪兩個(gè)點(diǎn)關(guān)于原點(diǎn)O對(duì)稱？A(-5,0),B(0,2),C(2,-1),D(2,0),E(0,5),F(-2,-1),G(-2,1)兩個(gè)點(diǎn)關(guān)于原點(diǎn)對(duì)稱時(shí)，它們坐標(biāo)符號(hào)相反，即點(diǎn)P(x,y)關(guān)于原點(diǎn)對(duì)稱點(diǎn)為P1(-x,-y)練習(xí)6/11xyo例1：如圖，利用關(guān)于原點(diǎn)對(duì)稱點(diǎn)坐標(biāo)特點(diǎn)，作出與⊿ABC關(guān)于原點(diǎn)對(duì)稱圖形。兩個(gè)點(diǎn)關(guān)于原點(diǎn)對(duì)稱時(shí)，它們坐標(biāo)符號(hào)相反，即點(diǎn)P(x,y)關(guān)于原點(diǎn)對(duì)稱點(diǎn)為P1(-x,-y)ABC例題講解7/11xyo解：點(diǎn)P(x,y)關(guān)于原點(diǎn)對(duì)稱點(diǎn)為P1(-x,-y)，所以⊿ABC三個(gè)頂點(diǎn)A(-3,1),B(-1,-1),C(-2,2)關(guān)于原點(diǎn)對(duì)稱點(diǎn)分別為A1(3,-1),B1(1,1),C1(2,-2),依次連接A1B1,

B1C1,

C1A1,就可得到與⊿ABC關(guān)于原點(diǎn)對(duì)稱⊿A1B1C1.ABCA1B1C1例題講解8/111．以下函數(shù)中，圖象一定關(guān)于原點(diǎn)對(duì)稱圖象是（）A．y=B．y=2x+1C．y=-2x+1D．以上三種都不可能2．假如點(diǎn)P（-3，1），那么點(diǎn)P（-3，1）關(guān)于原點(diǎn)對(duì)稱點(diǎn)P/坐標(biāo)是P/_______．3．寫出函數(shù)y=-與y=含有一個(gè)共同性質(zhì)________（用對(duì)稱觀點(diǎn)寫）．練習(xí)9/114、畫⊿AOB關(guān)于原點(diǎn)對(duì)稱⊿A’OB’

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