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Conic Sections Test - 49

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Conic Sections Test - 49
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  • Question 1
    1 / -0
    The eccentricity of the conic $$9x^{2} + 25y^{2} = 225$$ is
    Solution
    Equation of the given ellipse is 

    $$9x^2+25y^2=225$$

    Dividing through out by $$225$$

    $$\dfrac {x^2}{25}+\dfrac {y^2}{9}=1$$

    Hence $$a^2=25$$ and $$b^2=9$$

    $$\therefore \ c=\sqrt {25-9}=\sqrt {16}=4$$

    eccentricity $$(e)=\dfrac {c}{a}=\dfrac {4}{5}$$
  • Question 2
    1 / -0
    The eccentricity of the conic $$9{x}^{2}-16{y}^{2}=144$$ is
    Solution

  • Question 3
    1 / -0
    The vertex of the parabola $$y^2 - 4y - x + 3 = 0$$ is
    Solution
    We have,

    $$y^2 - 4y - x + 3 = 0$$
    $$\Rightarrow (y-2)^2 - 4 - x+3 = 0$$

    $$\Rightarrow (y-2)^2 = (x+1)$$

    $$\therefore$$ Vertex of the parabola $$= (-1,2)$$
  • Question 4
    1 / -0
     The equation $$5x^2 + y^2 + y = 8$$ represents 
    Solution
    We have,
    $$5x^2 + y^2 + y = 8$$
    $$\Rightarrow 5x^2 + \left(y + \dfrac{1}{2}\right)^2 - \left(\dfrac{1}{2}\right)^2 = 8$$

    $$\Rightarrow 5x^2 + \left(y + \dfrac{1}{2}\right)^2 = \dfrac{33}{8}$$

    $$\Rightarrow \dfrac{\dfrac{5x^2}{33}}{8} + \dfrac{\dfrac{\left(y+\dfrac{1}{2}\right)^2}{33}}{8} = 1$$

    $$\Rightarrow \dfrac{x^2}{\left(\dfrac{33}{40}\right)} + \dfrac{\left(y+\dfrac{1}{2}\right)^2}{\left(\dfrac{33}{8}\right)} = 1$$
    which is sn equation of ellipse.
  • Question 5
    1 / -0
    Write the length of the latus-rectum of the hyperbola $$16{x}^{2}-9{y}^{2}=144$$
    Solution

  • Question 6
    1 / -0
    The equation of the circle with centre $$(2, 2)$$ which passes through $$(4,5)$$ is 
    Solution
    Radius of circle is $$\sqrt{(4-2)^2+(5-2)^2}=\sqrt{13}$$ So, equation of circle is
    $$(x-2)^2+(y-2)^2=13$$
    $$\Rightarrow x^2+4-4x+y^2+4-4y=13$$
    $$\Rightarrow x^2+y^2-4x-4y-5=0$$
  • Question 7
    1 / -0
    The centre of the ellipse $$4x^2 + y^2 - 8x + 4y - 8 = 0$$ is
    Solution
    We have,

    $$4x^2 + y^2 - 8x + 4y - 8 = 0$$
    $$\Rightarrow (4x^2 - 8x) + (y^2 + 4y)-8=0$$
    $$\Rightarrow (4x^2 - 2x) + (y^2 + 4y)-8=0$$

    $$\Rightarrow 4[(x-1)^2 - 1]+[(y + 2)^2 - 4]-8=0$$
    $$\Rightarrow  4(x-1)^2 -4 + (y + 2)^2 - 4 -8=0$$

    $$\Rightarrow  4(x-1)^2 + (y+2)^2 = 16$$

    $$\Rightarrow  \dfrac{(x-1)^2}{4} + \dfrac{(y+2)^2}{16} = 1$$

    $$\therefore$$ Centre $$= (1,2)$$
  • Question 8
    1 / -0
    The latus-rectum of the hyperbola $$16{x}^{4}-9{y}^{2}=144$$ is
    Solution

  • Question 9
    1 / -0
    Write the eccentricity of the hyperbola whose latus-rectum is half of its transverse axis.
    Solution

  • Question 10
    1 / -0
    The eccentricity of the ellipse $$\dfrac{(x-1)^2}{2} + \left(y + \dfrac{3}{4}\right)^2 = \dfrac{1}{16}$$ is
    Solution
    $$\dfrac{(x-1)^2}{2} + \left(y + \dfrac{3}{4}\right)^2 = \dfrac{1}{16}$$

    $$\Rightarrow 8(x-1)^2 + 16\left(y +\dfrac{3}{4}\right)^2 = 1$$

    $$\Rightarrow \dfrac{(x-1)^2}{\dfrac{1}{8}} + \dfrac{\left(y + \dfrac{3}{4}\right)^2}{\dfrac{1}{16}} = 1$$

    $$\therefore a^2 = \dfrac{1}{8}$$ and $$b^2 = \dfrac{1}{16}$$

    $$\Rightarrow a = \dfrac{1}{2\sqrt{2}}$$ and $$b = \dfrac{1}{4}$$

    $$\therefore e = \sqrt{1 - \dfrac{b^2}{a^2}}$$         $$[\because a > b]$$

    $$= \sqrt{1-\dfrac{\dfrac{1}{16}}{\dfrac{1}{8}}} = \sqrt{1 - \dfrac{1}{2}} = \dfrac{1}{\sqrt{2}}$$
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