人教版九年級(jí)數(shù)學(xué)上冊(cè)《關(guān)于原點(diǎn)對(duì)稱的點(diǎn)的坐標(biāo)》旋轉(zhuǎn)PPT教學(xué)課件,共18頁(yè)。
學(xué)習(xí)目標(biāo)
1.掌握關(guān)于原點(diǎn)對(duì)稱的點(diǎn)的坐標(biāo)的關(guān)系.
2.能在平面直角坐標(biāo)系中畫出已知圖形關(guān)于原點(diǎn)對(duì)稱的圖形.
復(fù)習(xí)引入
平面直角坐標(biāo)系中有一點(diǎn)P(2,3),點(diǎn)P關(guān)于x軸的對(duì)稱點(diǎn)的坐標(biāo)是什么?點(diǎn)P關(guān)于y軸的對(duì)稱點(diǎn)的坐標(biāo)是什么?
點(diǎn)P關(guān)于x軸的對(duì)稱點(diǎn)坐標(biāo)為(2,-3),
點(diǎn)P關(guān)于y軸的對(duì)稱點(diǎn)坐標(biāo)為(-2,3).
在平面直角坐標(biāo)系中,關(guān)于x軸對(duì)稱的點(diǎn)的橫坐標(biāo)相等,縱坐標(biāo)互為相反數(shù).
關(guān)于y軸對(duì)稱的點(diǎn)的縱坐標(biāo)相等,橫坐標(biāo)互為相反數(shù)
導(dǎo)入新知
關(guān)于原點(diǎn)對(duì)稱的點(diǎn)的坐標(biāo)
如圖,在直角坐標(biāo)系中,作出下列已知點(diǎn)關(guān)于原點(diǎn)O的對(duì)稱點(diǎn),并寫出它們的坐標(biāo).
A(4,0),B(0,-3),C(2,1),D(-1,2),E(-3,-4).
關(guān)于原點(diǎn)對(duì)稱的點(diǎn)的坐標(biāo)的規(guī)律:
兩個(gè)點(diǎn)關(guān)于原點(diǎn)對(duì)稱時(shí),它們的坐標(biāo)符號(hào)相反,即點(diǎn)P(x,y)關(guān)于原點(diǎn)的對(duì)稱點(diǎn)為P′(-x,-y).
作關(guān)于原點(diǎn)對(duì)稱的圖形的步驟:
(1)寫出各點(diǎn)關(guān)于原點(diǎn)對(duì)稱的點(diǎn)的坐標(biāo);
(2)在坐標(biāo)平面內(nèi)描出這些對(duì)稱點(diǎn);
(3)參照原圖形順次連接各點(diǎn),即得到所求作的對(duì)稱圖形.
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