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8.3 抛物线

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8.3 抛物线. 1 .抛物线的定义 平面内与一个定点 F 和一条定直线 l ( F ∉ l ) 的距离 的点的轨迹叫做抛物线. 要注意点 F 不在直线 l 上,否则轨迹不是抛物线,而是一条直线. 相等. 2 .抛物线的标准方程和几何性质 ( 如下表所示 ). 误区警示 关于抛物线的标准方程 由于选取坐标系时,坐标轴有四种不同的方向,因此抛物线的标准方程有四种不同的形式,这四种标准方程的共同点在于: (1) p 的几何意义:焦参数 p 是焦点到准线的距离,所以 p 恒为正数. - PowerPoint PPT Presentation

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  • 1Fl(Fl)Fl.

  • 2()

    y22px(p>0)y22px(p>0)

  • y22px(p>0)y22px(p>0)x0yRx0yRxO(0,0)e1

  • x22py(p>0)x22py(p>0)

  • x22py(p>0)x22py(p>0)y0xRy0xRyO(0,0)e1

  • (1)ppp(2). (3)

  • Px20M(40)2P()ABC DPx4M(4,0)D.D[1]

  • Pxy40M(2,2)P()A BC DM(2,2)xy40|PM|Pxy40PMxy40A.A

  • (1,0)x1()Ax2y21 Bx2y21Cy24x Dx0(xy)x(1) y24xC.CC(1,0)x1C(1,0)x1p2y24x.

  • [2]

  • Py24xQx2(y4)21PQP()

    A5

    B8 C.eq \r(17)1 D.eq \r(5)2

    []y24xF(1,0)x2(y4)21C(0,4)Pdd|PF||PQ|d|PQ||PF|(|PC|1)|PF||CF|1eq \r(17)1.

  • 9Q

  • [3]

  • [4]

    eq \f(x2,m)eq \f(y2,n)1(mn0)2y24xmn

    ()

    A.eq \f(3,16)

    B.eq \f(3,8)

    C.eq \f(16,3)

    D.eq \f(8,3)

  • A

    eq \b\lc\{\rc\ (\a\vs4\al\co1(\f(\r(mn),\r(m))2,\r(mn)1))eq \b\lc\{\rc\ (\a\vs4\al\co1(m\f(1,4),n\f(3,4))) .

    mneq \f(3,16).A.

  • y22px 1p ()A2B2 C4D4D

    a26b22ceq \r(a2b2)2

    (2,0)eq \f(p,2)2p4.

  • Cy28xFxKAC|AK| |AF|AFK()A4 B8 C16 D32y28xF(2,0)x2K(2,0)[5]

  • (x2)2y22[(x2)2y2]y2x212x4y28xx2y4

    B|AK| |AF|.

  • [6]

    [1]yax21yxa()

    A.eq \f(1,8)B.eq \f(1,4)

    C.eq \f(1,2)

    D1

  • B

    1yax21yxeq \b\lc\{\rc\ (\a\vs4\al\co1(yax21,yx))ax2x10(1)24a0aeq \f(1,4).

    2(x0x0)yax21y|xx02ax02ax01.

    (x0x0)x0axeq \o\al(2,0)1

    aeq \f(1,4).B.

  • P 0 4 y2=2x 3

  • [7]

    ABy22px(p>0)FA(x1y1)B(x2y2)

    (1)x1x2eq \f(p2,4)

    (2)|AB|x1x2peq \f(2p,sin2)(ABx)

    (3)SAOBeq \f(p2,2sin)

    (4)eq \f(1,|AF|)eq \f(1,|BF|)

    (5)AB

  • .

  • (1)y22px(p>0)Feq \b\lc\(\rc\)(\a\vs4\al\co1(\f(p,2)0))

    ykeq \b\lc\(\rc\)(\a\vs4\al\co1(x\f(p,2)))(k0)

    eq \b\lc\{\rc\ (\a\vs4\al\co1(yk\b\lc\(\rc\)(\a\vs4\al\co1(x\f(p,2))),y22px))xky22pykp20

    y1y2p2x1x2eq \f((y1y2)2,4p2)eq \f(p2,4).

    kxeq \f(p,2)

    y1py2py1y2p2x1x2eq \f(p2,4).

    y1y2p2x1x2eq \f(p2,4).

  • (2)|AF|Axeq \f(p,2).

    |AF|x1eq \f(p,2)|BF|x2eq \f(p,2).

    |AB||AF||BF|x1x2p.

    ykeq \b\lc\(\rc\)(\a\vs4\al\co1(x\f(p,2)))xeq \f(1,k)yeq \f(p,2).

    x1x2eq \f(1,k)(y1y2)p

    y1y2eq \f(2p,k).x1x2eq \f(2p,k2)p

    |AB|eq \f(2p,k2)2p2peq \b\lc\(\rc\)(\a\vs4\al\co1(1\f(1,k2)))2peq \b\lc\(\rc\)(\a\vs4\al\co1(1\f(1,tan2)))eq \f(2p,sin2) .

  • (3)

    SAOBSAOFSBOF

    eq \f(1,2)|OF||AF|sineq \f(1,2)|OF||BF|sin

    eq \f(1,2)|OF|sin(|AF||BF|)

    eq \f(1,2)|OF||AB|sin

    eq \f(1,2)eq \f(p,2)eq \f(2p,sin2)sineq \f(p2,2sin).

  • (4)eq \f(1,|AF|)eq \f(1,|BF|)eq \f(1,x1\f(p,2))eq \f(1,x2\f(p,2))

    eq \f(x1x2p,x1x2\f(p,2)(x1x2)\f(p2,4))

    x1x2eq \f(p2,4)

    eq \f(1,|AF|)eq \f(1,|BF|)eq \f(2,p).

    (5)ABM(x0y0)AMBCND

    |MN|eq \f(1,2)(|AC||BD|)eq \f(1,2)(|AF||BF|)

    eq \f(1,2)|AB|. AB

  • (1)(). ANB90CDABF. (2)

  • y22px(p>0)FP1(x1y1)P2(x2y2)P3(x3y3)2x2x1x3()A|FP1||FP2||FP3|B|FP1|2|FP2|2|FP3|2C2|FP2||FP1||FP3|D|FP2|2|FP1||FP3|

  • 2x2x1x3p

    P1P2P32|FP2||FP1||FP3|.C

  • [8]

    y22px(p>0)1ABAB2()

    Ax1 Bx1 Cx2

    Dx2

    []A(x1y1)B(x2y2)AB(eq \f(x1x2,2)eq \f(y1y2,2))eq \f(y1y2,2)2eq \b\lc\{\rc\ (\a\vs4\al\co1(y\o\al(2,1)2px1,y\o\al(2,2)2px2))yeq \o\al(2,1)yeq \o\al(2,2)2p(x1x2)kABeq \f(y1y2,x1x2)eq \f(2p,y1y2)eq \f(p,2)kAB1p2y24xx1B.

  • [9]

  • Cyax21(a0)lyx0a________A(x1y1)B(x2y2)Cl(x1x2)AByxb.

    x1x214a(1b)>0.ABM(x0y0)

  • x0eq \f(x1x2,2)eq \f(1,2a)y0x0beq \f(1,2a)b.

    Mleq \f(1,2a)eq \f(1,2a)b0

    beq \f(1,a)a>eq \f(3,4).

  • [10]

    xOyly24xAB.

    (1)leq \o(OA,\s\up6())eq \o(OB,\s\up6())________

    (2)eq \o(OA,\s\up6())eq \o(OB,\s\up6())4l________

  • (1)(1,0)lxty1y24xxy24ty40A(x1y1)B(x2y2)y1y24ty1y24x1x2y1y2(ty11)(ty21)y1y2t2y1y2t(y1y2)1y1y24t24t2143.

  • (2)lxtyby24xxy24ty4b0A(x1y1)B(x2y2)y1y24ty1y24b. x1x2y1y2(ty1b)(ty2b)y1y2t2y1y2bt(y1y2)b2y1y24bt24bt2b24bb24b.b24b4b24b40b2.l(2,0)(1)3(2)(2,0)

  • ABCy22px(p>0)FABxxD.

    (1)DFABeq \f(,4)eq \f(\o(OA,\s\up6())\o(OB,\s\up6()),p2)(O)

    (2)|AF||BF|8ABQ(6,0)C

  • []A(x1y1)B(x2y2)

    (1)AByxeq \f(p,2)

    eq \b\lc\{\rc\ (\a\vs4\al\co1(y22px,yx\f(p,2)))x23pxeq \f(p2,4)0

    x1x23px1x2eq \f(p2,4).

    eq \f(\o(OA,\s\up6())\o(OB,\s\up6()),p2)eq \f(x1x2y1y2,p2)eq \f(x1x2\b\lc\(\rc\)(\a\vs4\al\co1(x1\f(p,2)))\b\lc\(\rc\)(\a\vs4\al\co1(x2\f(p,2))),p2)

    eq \f(2x1x2\f(p,2)(x1x2)\f(p2,4),p2)eq \f(2\f(p2,4)\f(p,2)3p\f(p2,4),p2)eq \f(3,4)

  • (2)xeq \f(p,2)|AF||BF|x1eq \f(p,2)x2eq \f(p,2)x1x2p8

    x1x28p

    Q(6,0)AB|QA||QB|

    (x16)2yeq \o\al(2,1)(x26)2yeq \o\al(2,2)

    yeq \o\al(2,1)2px1yeq \o\al(2,2)2px2

    (x16)22px1(x26)22px2

    (x1x2)(x1x2122p)0

    x1x2x1x2122p8p122p0

    p4y28x.