The line x = 2y intersects the ellipse x2/4 + y2= 1at the points P and...
Solving the given equations then common points are

Eqn. of Circle PQ as
diameter
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The line x = 2y intersects the ellipse x2/4 + y2= 1at the points P and...
Given:
- The line x = 2y intersects the ellipse x^2/4 + y^2 = 1 at the points P and Q.
To find:
- The equation of the circle with PQ as diameter.
Solution:
Step 1: Find the coordinates of points P and Q:
- Substitute x = 2y in the equation of the ellipse:
(2y)^2/4 + y^2 = 1
4y^2/4 + y^2 = 1
5y^2/4 = 1
y^2 = 4/5
y = ±√(4/5)
- Since x = 2y, we can substitute the value of y in x = 2y:
x = 2(±√(4/5))
x = ±2√(4/5)
- Therefore, the coordinates of points P and Q are (2√(4/5), ±√(4/5)).
Step 2: Find the midpoint of PQ:
- The midpoint of a line segment with endpoints (x1, y1) and (x2, y2) is given by the formula:
Midpoint = ((x1 + x2)/2, (y1 + y2)/2)
- Applying this formula, we can find the coordinates of the midpoint of PQ:
Midpoint = ((2√(4/5) + -2√(4/5))/2, (√(4/5) + -√(4/5))/2)
Midpoint = (0, 0)
Step 3: Find the radius of the circle:
- The radius of a circle with diameter PQ is the distance from the midpoint to one of the endpoints.
- Using the distance formula, we can calculate the radius:
Radius = √((x1 - x2)^2 + (y1 - y2)^2)
Radius = √((0 - 2√(4/5))^2 + (0 - √(4/5))^2)
Radius = √((-2√(4/5))^2 + (-√(4/5))^2)
Radius = √(4(4/5) + (4/5))
Radius = √(16/5 + 4/5)
Radius = √(20/5)
Radius = √4
Radius = 2
Step 4: Write the equation of the circle:
- The equation of a circle with center (h, k) and radius r is given by the formula:
(x - h)^2 + (y - k)^2 = r^2
- Since the midpoint of PQ is (0, 0) and the radius is 2, the equation of the circle is:
(x - 0)^2 + (y - 0)^2 = 2^2
x^2 + y^2 = 4
Final Answer:
The equation of the circle with PQ as diameter is x^2 + y^2 = 4, which is option D.