Question:
The length of latus rectum o f the parabola $4y^2 + 3x + 3y + 1 = 0$ is
The length of latus rectum o f the parabola $4y^2 + 3x + 3y + 1 = 0$ is
Updated On: Apr 8, 2024
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The Correct Option is D
Solution and Explanation
We have, $4 y^{2}+3 x+3 y+1=0$
$\Rightarrow 4 y^{2}+3 y=-3 x-1$
$\Rightarrow y^{2}+\frac{3}{4} y=-\frac{3}{4} x-\frac{1}{4}$
$\Rightarrow y^{2}+\frac{3}{4} y+\frac{9}{64}=-\frac{3}{4} x-\frac{1}{4}+\frac{9}{64}$
$\Rightarrow\left(y+\frac{3}{8}\right)^{2}=-\frac{3}{4}\left(x+\frac{7}{48}\right)$
$\therefore$ Length of latusrectum $=\frac{3}{4}$
$\Rightarrow 4 y^{2}+3 y=-3 x-1$
$\Rightarrow y^{2}+\frac{3}{4} y=-\frac{3}{4} x-\frac{1}{4}$
$\Rightarrow y^{2}+\frac{3}{4} y+\frac{9}{64}=-\frac{3}{4} x-\frac{1}{4}+\frac{9}{64}$
$\Rightarrow\left(y+\frac{3}{8}\right)^{2}=-\frac{3}{4}\left(x+\frac{7}{48}\right)$
$\therefore$ Length of latusrectum $=\frac{3}{4}$
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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.