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Grade 11IIT JEE Entrance Exam

The tangent to the parabola at the vertex V and any point P meet at Q. If S be the focus then SP,SQ,SV are in. 1)AP 2)GP 3)HP 4)AGP

Profile image of Aman Ashish
9 Years agoGrade 11
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1 Answer

Profile image of Nishant Vora
9 Years ago

To analyze the relationship between the segments SP, SQ, and SV in the context of a parabola, let's first clarify the elements involved. We have a parabola with a vertex at point V, a focus at point S, and an arbitrary point P on the parabola. The tangent line at the vertex V intersects the line segment connecting the focus S to the point P at point Q. The question asks us to determine the nature of the ratios SP, SQ, and SV.

Understanding the Components

In this scenario, we should consider the geometric properties of a parabola. The key features are:

  • Vertex (V): The highest or lowest point of the parabola, depending on its orientation.
  • Focus (S): A fixed point from which distances to points on the parabola are measured.
  • Tangent Line: A straight line that touches the parabola at just one point, in this case, the vertex.
  • Point (P): Any point on the parabola that we can choose to examine.
  • Point (Q): The intersection of the tangent at V with the line segment SP.

Geometric Relationships

To delve into the relationships between the segments, we can apply some principles from analytic geometry. The parabola can be described by the equation \(y^2 = 4px\), where p is the distance from the vertex to the focus. Here, the focus S is at (p, 0) and the vertex V is at (0, 0).

When we draw the tangent line at the vertex, it will be horizontal (y = 0) for this standard orientation. The line extending from S to any point P on the parabola will have varying slopes, depending on P's position.

Analyzing the Ratios

Now, let’s consider the segments:

  • SV: The distance from the focus to the vertex, which is constant and equal to p.
  • SP: The distance from the focus to point P, which varies depending on where P is located on the parabola.
  • SQ: The distance from the focus to point Q, the intersection of the tangent line and line segment SP.

Because the parabola has the property that any point P on it is equidistant from the focus S and the directrix, we can derive that the relationship between these segments follows a specific pattern. When we set up the ratios SP, SQ, and SV, we find that they do not vary linearly. Instead, they exhibit a harmonic progression.

Final Thoughts on the Progression

In harmonic progression (HP), the reciprocals of the terms form an arithmetic progression. This means that if you take the reciprocals of SP, SQ, and SV, those values will behave linearly. Given the properties of the parabola and the distances involved, it becomes clear that:

SP, SQ, and SV are in Harmonic Progression (HP).

To summarize, the distances we have identified—SP, SQ, and SV—are related such that they demonstrate harmonic progression due to the nature of the parabola and the geometric properties involving the focus and tangent lines. This is a fascinating aspect of conic sections that showcases the beauty of mathematical relationships in geometry.