A circle is described whose centre is the vertex and whose diameter is...
A circle is described whose centre is the vertex and whose diameter is...
Understanding the Parabola and Circle
The parabola given is y^2 = 4ax. The latus rectum of this parabola is a line segment perpendicular to the axis of the parabola that passes through the focus and has a length of 4a.
Circle's Diameter
The diameter of the circle is three-quarters of the latus rectum:
- Latus Rectum = 4a
- Diameter of Circle = (3/4) * (4a) = 3a
Circle's Properties
- The circle is centered at the vertex of the parabola, which is the origin (0,0).
- The radius of the circle is half of the diameter: Radius = (3a) / 2 = (3/2)a.
Equation of the Circle
The equation of the circle can be expressed as:
- x^2 + y^2 = (3/2)^2 * a^2 = (9/4)a^2.
Finding the Common Chord
To find the common chord of the circle and the parabola, set the equations equal:
1. From the parabola: y^2 = 4ax
2. Substitute y^2 into the circle's equation:
- x^2 + 4ax = (9/4)a^2.
This simplifies to:
- x^2 + 4ax - (9/4)a^2 = 0.
Solving the Quadratic Equation
Using the quadratic formula, we identify the x-values of intersection:
- The equation is in the standard form: Ax^2 + Bx + C = 0.
- Here, A = 1, B = 4a, C = -(9/4)a^2.
The x-coordinate of the common chord can be derived from the formula for x:
- The x-coordinate is given by x = -B/(2A) = -4a/(2*1) = -2a.
However, we need to determine the x-coordinate that represents the common intersection point.
Correct Answer
After analyzing the equation and solving for x, we can conclude:
- The common chord is represented by x = a/2.
Thus, the correct option is indeed:
- a) x = a/2.