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Parabola Class 11 Notes Maths Chapter 11

  • The general equation of a conic is ax2 + 2hxy + by2 + 2gx + 2fy +c =0. Here if e =1 and D≠ 0, then it represents a parabola. 
  • The general equation of parabola is (y-y0)= (x-x0), which has its vertex at (x0, y0). 
  • The general equation of parabola with vertex at (0, 0) is given by y2 = 4ax, and it opens rightwards.
  • The parabola x2 = 4ay opens upwards.
  • The equation y2 = 4ax is considered to be the standard equation of the parabola for which the various components areParabola Class 11 Notes Maths Chapter 111. Vertex at (0,0)
    2. Directrix is x+a = 0
    3. Axis is y = 0
    4. Focus is (a, 0)
    5. Length of latus rectum = 4a
    6. Ends of latus rectum are L(a, 2a) and L’(a, -2a)
  • The parabola y = a(x – h)2 + khas its vertex at (h, k)
  • The perpendicular distance from focus on directrix is half the length of latus rectum
  • Vertex is the middle point of the focus and the point of intersection of directrix and axis
  • Two parabolas are said to be equal if they have the same latus rectum
  • The point (x1, y1) lies outside, on or inside the parabola y2 = 4ax, according as the expression y12 = 4ax1 is positive, zero or negative.
  • Length of the chord intercepted by the parabola on the line y = mx + c is (4/m2) √a(1+m2) (a-mc)
  • Length of the focal chord which makes an angle δ with the x-axis is 4a cosec2δ
  • In parametric form, the parabola is represented by the equations x = at2 and y =2at
  • The equation of a chord joining t1 and t2 is given by 2x – (t1 + t2) y + 2at1t2 = 0
  • If a chord joining t1, t2 and t3, t4 pass through a point (c, 0) on the axis, then t1t2 = t3t4 = -c/a
  • Tangents to the parabola y2 = 4ax
    1. yy1 = 2a(x+x1) at the point (x1, y1)
    2. y = mx + a/m ( m ≠ 0) at (a/m2, 2a/m)
    3. ty = x+at2 at (at2, 2at)
  • Normals to the parabola y2 = 4ax
    1. y-y= -y1/ 2a(x-x1) at the point (x1, y1)
    2. y = mx -2am – am3 at (am2, -2am)
    3. y + tx = 2at +at3 at (at2, 2at)
  • The equation of the director circle to the parabola is x + a = 0 which is same as the equation of the directrix
  • The circle circumscribing the triangle formed by any three tangents to a parabola passes through the focus.
  • The orthocenter of any triangle formed by three tangents to a parabola y2 = 4ax lies on then directrix and has the coordinates –a, a(t+ t2 + t3 + t1t2t3).
  • The area of the triangle formed by three points on a parabola is twice the area of the triangle formed by the tangents at these points.
  • A circle circumscribing the triangle formed by three co-normal points passes through the vertex of the parabola and its equation is given by 2(x2 + y2)– 2(h+2a)x - ky =0
    The two vital parabolas along with their basic components like vertex and directrix are tabulated below:Parabola Class 11 Notes Maths Chapter 11
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FAQs on Parabola Class 11 Notes Maths Chapter 11

1. What is a parabola?
Ans. A parabola is a U-shaped curve that is formed by the graph of a quadratic equation. It is symmetric about a line called the axis of symmetry and has a vertex, which is the lowest or highest point on the curve.
2. How do you identify the equation of a parabola?
Ans. To identify the equation of a parabola, you need to know its vertex and whether it opens upwards or downwards. If the vertex is at the point (h, k) and the parabola opens upwards, the equation can be written as y = a(x - h)^2 + k. If it opens downwards, the equation would be y = -a(x - h)^2 + k, where 'a' is a constant.
3. How can you find the vertex of a parabola?
Ans. The vertex of a parabola can be found using the formula (-b/2a, f(-b/2a)), where 'a' and 'b' are the coefficients of the quadratic equation in the form ax^2 + bx + c = 0. By substituting this value of 'x' into the equation, you can find the corresponding 'y' coordinate of the vertex.
4. How can you determine if a parabola opens upwards or downwards?
Ans. The coefficient 'a' in the quadratic equation determines whether a parabola opens upwards or downwards. If 'a' is positive, the parabola opens upwards, and if 'a' is negative, the parabola opens downwards.
5. Can a parabola intersect the x-axis at more than two points?
Ans. No, a parabola can intersect the x-axis at a maximum of two points. This is because a quadratic equation can have a maximum of two real roots. If the discriminant of the quadratic equation is greater than zero, it will intersect the x-axis at two distinct points. If the discriminant is zero, it will intersect the x-axis at a single point, which is the vertex of the parabola. If the discriminant is negative, the parabola will not intersect the x-axis.
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