3) Let the coordinates of point P be (x, y).
Using the distance formula:
PA = sqrt[ (x - 4)2 + (y - -1)2 ] ---> PA = sqrt[ (x - 4)2 + (y + 1)2 ] ---> PA2 = (x - 4)2 + (y + 1)2
PB = sqrt[ (x - 6)2 + (y - 2)2 ] ---> PB = sqrt[ (x - 6)2 + (y +- 2)2 ] ---> PB2 = (x - 6)2 + (y - 2)2
PC = sqrt[ (x - -1)2 + (y - 2)2 ] ---> PC = sqrt[ (x + 1)2 + (y - 2)2 ] ---> PC2 = (x + 1)2 + (y - 2)2
Combining these:
PA2 + PB2 + PC2 = (x - 4)2 + (y + 1)2 + (x - 6)2 + (y - 2)2 + (x + 1)2 + (y - 2)2
= (x2 - 8x + 16) + (y2 + 2y + 1) + (x2 - 12x + 36) + (y2 - 4y + 4) + (x2 + 2x + 1) + (y2 - 4y + 4)
= 3x2 - 18x + 3y2 - 6y + 62
= (3x2 - 18x ) + 3y2 - 6y ) + 62
= 3(x2 - 6x ) + 3(y2 - 2y ) + 62
= 3(x2 - 6x + 9) + 3(y2 - 2y + 1) + 32
= 3(x - 3)2 + 3(y - 1)2 + 32
Let the coordinates of X be (a,b) ---> PX = sqrt[ (x - a)2 + (y- b)2 ] ---> PX2 = (x - a)2 + (y- b)2
3PX2 + k = 3[ (x - a)2 + (y- b)2 ] + k = 3(x - a)2 + 3(y - b)2 + k
Setting these two equal to each other: 3(x - 3)2 + 3(y - 1)2 + 32 = 3(x - a)2 + 3(y - b)2 + k
tells me that a = 3, b = 1, and k = 32