數(shù)學(xué)2312中心對(duì)稱第3課時(shí)課件人教新課標(biāo)九年級(jí)上42

1、在平面直角坐標(biāo)系中畫出下列各點(diǎn)在平面直角坐標(biāo)系中畫出下列各點(diǎn)關(guān)于關(guān)于x x軸的對(duì)稱點(diǎn)軸的對(duì)稱點(diǎn). .31425-2-4-1-301 2 3 4 5-4 -3 -2 -1b (-4, 2)c(3, -4)b (-4, -2)c(3, 4)思考：思考：關(guān)于關(guān)于x軸軸對(duì)稱的點(diǎn)的坐標(biāo)對(duì)稱的點(diǎn)的坐標(biāo)具有怎樣的關(guān)系？具有怎樣的關(guān)系？在平面直角坐標(biāo)系中畫出下列各點(diǎn)關(guān)于y軸的對(duì)稱點(diǎn).31425-2-4-1-301 2 3 4 5-4 -3 -2 -1b (-4, 2)c(3, -4)b (4, 2)c(-3, -4)小結(jié)：小結(jié)：在平面直角坐標(biāo)系中，關(guān)于在平面直角坐標(biāo)系中，關(guān)于x軸對(duì)稱的點(diǎn)軸對(duì)稱的點(diǎn)橫坐標(biāo)橫坐標(biāo)

2、相等相等, ,縱坐標(biāo)互為縱坐標(biāo)互為相相反數(shù)反數(shù). .關(guān)于關(guān)于y軸對(duì)稱的點(diǎn)軸對(duì)稱的點(diǎn)橫坐標(biāo)互為橫坐標(biāo)互為相相反數(shù)反數(shù), ,縱坐標(biāo)縱坐標(biāo)相等相等. .點(diǎn)（點(diǎn)（x, y）關(guān)于關(guān)于x軸對(duì)稱的點(diǎn)的坐標(biāo)為軸對(duì)稱的點(diǎn)的坐標(biāo)為_.點(diǎn)（點(diǎn)（x, y）關(guān)于關(guān)于y軸對(duì)稱的點(diǎn)軸對(duì)稱的點(diǎn)的坐標(biāo)為的坐標(biāo)為_.(x,(x,y)y)( (x,y)x,y)在平面直角坐標(biāo)系中畫出下列各點(diǎn)關(guān)于原點(diǎn)的對(duì)稱點(diǎn).31425-2-4-1-301 2 3 4 5-4 -3 -2 -1c (-3, 4)c(3, -4)b (4, 2)b(-4,-2)小結(jié)：小結(jié)：在平面直角坐標(biāo)系中，關(guān)于原點(diǎn)對(duì)稱的點(diǎn)在平面直角坐標(biāo)系中，關(guān)于原點(diǎn)對(duì)稱的點(diǎn)橫坐標(biāo)互為

3、相反數(shù)橫坐標(biāo)互為相反數(shù),縱坐標(biāo)互為相反數(shù)縱坐標(biāo)互為相反數(shù).點(diǎn)（點(diǎn)（x, y）關(guān)于）關(guān)于x軸對(duì)稱軸對(duì)稱的點(diǎn)的坐標(biāo)為的點(diǎn)的坐標(biāo)為_.(-x,(-x,y)y)1、完成下表、完成下表.已知點(diǎn)已知點(diǎn)(2,-3)(-1,2)(-6,-5) (0,-1.6) (4,0)關(guān)于關(guān)于x軸的對(duì)稱點(diǎn)軸的對(duì)稱點(diǎn)關(guān)于原點(diǎn)的對(duì)稱點(diǎn)關(guān)于原點(diǎn)的對(duì)稱點(diǎn)(-2, 3)(2, 3)(-1,-2)(1, -2) (6, 5)(-6, 5)(0, 1.6)(0,1.6)(-4,0)(4,0)2、已知點(diǎn)、已知點(diǎn)p(2a+b,-3a)與點(diǎn)與點(diǎn)p(8,b+2).若點(diǎn)若點(diǎn)p與點(diǎn)與點(diǎn)p關(guān)于關(guān)于x軸對(duì)稱，則軸對(duì)稱，則a=_ b=_.若點(diǎn)若點(diǎn)p與點(diǎn)與

4、點(diǎn)p關(guān)于關(guān)于y軸對(duì)稱，則軸對(duì)稱，則a=_ b=_.若點(diǎn)若點(diǎn)p與點(diǎn)與點(diǎn)p關(guān)于原點(diǎn)對(duì)稱，則關(guān)于原點(diǎn)對(duì)稱，則a=_ b=_.練練 習(xí)習(xí)46-202-1.2-5.63.下列圖象中下列圖象中,一定關(guān)于原點(diǎn)對(duì)稱的圖象是一定關(guān)于原點(diǎn)對(duì)稱的圖象是( )a.y=1/x b.y=2x+1 c.y=-2x+1 d.以上以上三種都有可能三種都有可能.例：已知例：已知abc的三個(gè)頂點(diǎn)的坐標(biāo)分別為的三個(gè)頂點(diǎn)的坐標(biāo)分別為a(-3，5),b(- 4，1),c(-1，3)，作出，作出abc關(guān)于關(guān)于原點(diǎn)對(duì)稱的圖形。原點(diǎn)對(duì)稱的圖形。解：點(diǎn)解：點(diǎn)a(-3,5),b(-4,1),a(-3,5),b(-4,1),c(-1,3)c(-1,

5、3)，關(guān)于，關(guān)于y y軸對(duì)稱軸對(duì)稱點(diǎn)的坐標(biāo)分別為點(diǎn)的坐標(biāo)分別為a(3,5), a(3,5), b(4,1),c(1,3).b(4,1),c(1,3).依依次連接次連接ab,bc,ca,ab,bc,ca,就得到就得到abcabc關(guān)于關(guān)于y y軸對(duì)軸對(duì)稱的稱的abc.abc.31425-2-4-1-301 2 3 4 5-4 -3 -2 -1acb-5abc1.四邊形四邊形abcd各頂點(diǎn)坐標(biāo)分別為各頂點(diǎn)坐標(biāo)分別為(5,0),(-2,3)，（，（-1,0) ,(-1,5),作出與四邊形作出與四邊形abcd關(guān)于原點(diǎn)關(guān)于原點(diǎn)o對(duì)稱的圖對(duì)稱的圖形形.2.平行四邊形平行四邊形,a(1,2), b(-4,2), c(-2,-5),求出第四個(gè)點(diǎn)求出第四個(gè)點(diǎn)d的坐標(biāo)的坐標(biāo).若平行四邊形在坐標(biāo)系內(nèi)關(guān)于原點(diǎn)對(duì)稱若平行四邊形在坐標(biāo)系內(nèi)關(guān)于原點(diǎn)對(duì)稱,已知點(diǎn)已知點(diǎn)a,點(diǎn)點(diǎn)b的坐標(biāo)不變的坐標(biāo)不變,點(diǎn)點(diǎn)c,點(diǎn)點(diǎn)d的坐標(biāo)又是什么的坐標(biāo)又是什么?1、學(xué)習(xí)了在平面直角坐標(biāo)系中，關(guān)于學(xué)習(xí)了在平面直角坐標(biāo)系中，關(guān)于x軸軸和和y軸對(duì)稱的點(diǎn)的坐標(biāo)的特點(diǎn)。軸對(duì)稱的點(diǎn)的坐標(biāo)的特點(diǎn)。關(guān)于關(guān)于x軸對(duì)稱的點(diǎn)軸對(duì)稱的點(diǎn)橫坐標(biāo)相等橫坐標(biāo)相等,縱坐標(biāo)互為縱坐標(biāo)互為相反數(shù)相反數(shù).關(guān)于關(guān)于y軸對(duì)稱的點(diǎn)軸對(duì)稱的