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Investigating a point in equilateral triangle (Posted on 2024-12-08) Difficulty: 3 of 5
In the interior of an equilateral triangle ABC a point P is chosen such that PA2 = PB2 + PC2. Find the measure of angle BPC.

No Solution Yet Submitted by Danish Ahmed Khan    
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Solution Solution Comment 1 of 1
Let A=(0,0), B(1/2,sqrt(3)/2), C=(1,0), and P=(x,y)
The the equation becomes
x^2 - y^2 = (x-1/2)^2+ (y-sqrt(3)/2)^2 + (x-1)^2 + y^2
which, after expanding and completing the square on x becomes
(x-3/2)^2+(y-sqrt(3)/2)^2 = 1
Which implies P can be anywhere on the arc of the circle of radius 1 centered at (3/2,sqrt(3)/2).  This circle contains B and C.  
Furthermore the arc from B to C is 60 degrees.  The arc external to the triangle is 300 degrees and central angle BPC = 150 degrees.

https://www.desmos.com/calculator/rsi6mqixax



  Posted by Jer on 2024-12-08 17:41:05
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