A particle is moving in the xy-plane along a curve C passing through the point (3, 3). The tangent to the curve C at the point P meets the x-axis at Q. If the y-axis bisects the segment PQ, then C is a parabola with
- Length of latus rectum 3
- Length of latus rectum 6
- \(Focus \bigg(\frac{4}{3},0\bigg)\)
- \(Focus \bigg(0,\frac{3}{4}\bigg)\)
The Correct Option is A
Solution and Explanation
\(2x-y \frac{dx}{dy} = 0\)
tangent at \(P:y-y =\frac{dy}{dx}(y-x)\)
\(∴ 2 \frac{dy}{y} = \frac{dx}{x}\)
\(⇒ 2Iny = Inx+Inc\)
\(⇒ y^2 = cx\)
At coordinates \((3, 3)\) curves pass through
Hence, \(c = 3\)
Therefore, the is parabola :
\(y^2 = 3x \)
So Length of latus rectum is \(3\).
Hence, the correct option is (A): Length of latus rectum is \(3\)
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Concepts Used:
Parabola
Parabola is defined as the locus of points equidistant from a fixed point (called focus) and a fixed-line (called directrix).
Standard Equation of a Parabola
For horizontal parabola
- Let us consider
- Origin (0,0) as the parabola's vertex A,
- Two equidistant points S(a,0) as focus, and Z(- a,0) as a directrix point,
- P(x,y) as the moving point.
- Let us now draw SZ perpendicular from S to the directrix. Then, SZ will be the axis of the parabola.
- The centre point of SZ i.e. A will now lie on the locus of P, i.e. AS = AZ.
- The x-axis will be along the line AS, and the y-axis will be along the perpendicular to AS at A, as in the figure.
- By definition PM = PS
=> MP2 = PS2
- So, (a + x)2 = (x - a)2 + y2.
- Hence, we can get the equation of horizontal parabola as y2 = 4ax.
For vertical parabola
- Let us consider
- Origin (0,0) as the parabola's vertex A
- Two equidistant points, S(0,b) as focus and Z(0, -b) as a directrix point
- P(x,y) as any moving point
- Let us now draw a perpendicular SZ from S to the directrix.
- Then SZ will be the axis of the parabola. Now, the midpoint of SZ i.e. A, will lie on P’s locus i.e. AS=AZ.
- The y-axis will be along the line AS, and the x-axis will be perpendicular to AS at A, as shown in the figure.
- By definition PM = PS
=> MP2 = PS2
So, (b + y)2 = (y - b)2 + x2
- As a result, the vertical parabola equation is x2= 4by.