SOLUTION: Find the locus of points P(x,y) such that the distance from P to (3,0) is twice its distance to (1,0).

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Question 1082339: Find the locus of points P(x,y) such that the distance from P to (3,0) is twice its distance to (1,0).
Found 2 solutions by josgarithmetic, ikleyn:
Answer by josgarithmetic(39618) About Me  (Show Source):
Answer by ikleyn(52797) About Me  (Show Source):
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Find the locus of points P(x,y) such that the distance from P to (3,0) is twice its distance to (1,0).
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Let (x,y) be the point of this locus.

Then 

sqrt%28%28x-3%29%5E2+%2B+%28y-0%29%5E2%29 = 2%2Asqrt%28%28x-1%29%5E2+%2B+%28y-0%29%5E2%29.    (1)

The left  side is the         distance from (x,y) to the point (3,0).
The right side is the doubled distance from (x,y) to the point (1,0).

Now square both sides of (1). You will get

%28x-3%29%5E2+%2B+y%5E2 = 4%2A%28x-1%29%5E2+%2B+4%2Ay%5E2.

Simplify:

x%5E2+-+6x+%2B+9+%2B+y%5E2 = 4x%5E2+-+8x+%2B+4+%2B+4y%5E2,

3x%5E2+%2B+3y%5E2+-+2x = 5,

%28x%5E2-%282%2F3%29x%29+%2B+3y%5E2 = 5%2F3,

%28x%5E2-%282%2F3%29x+%2B+%281%2F3%29%5E2%29+%2B+y%5E2 = 5%2F3+%2B+%281%2F3%29%5E2,

%28x-1%2F3%29%5E2+%2B+y%5E2 = 16%2F9,

%28x-1%2F3%29%5E2+%2B+y%5E2 = %284%2F3%29%5E2.

It is the equation of the circle of the radius 4%2F3 with the center at the point (1%2F3,0).

Answer. The locus under the question is the circle of the radius 4%2F3 with the center at the point (1%2F3,0).




Circle %28x-1%2F3%29%5E2+%2B+y%5E2 = %284%2F3%29%5E2