In triangle ABC, point X is on side BC such that AX=13, BX=14, CX=4, and the circumcircles of triangles ABX and ACX have the same radius. Find the area of triangle ABC.

Guest May 30, 2020

#1**0 **

I placed the diagram on a coordinate axis, with P(0,0), C(4,0), and B(-14,0).

Since PA = 13, it is on a circle with center P and radius 13: x2 + y2 = 13

-- I called the x-value of this point 'a', so the y-value became sqrt(169 - a2).

I used the theorem that the center of a circle is on the perpendicular bisectors of the chords.

Since one chord is BP, its midpoint has x-value -7 and its y-value is on the line x = -7.

Since another chord is PC, its midpoint has x-value 2 and its y-value is on the line x = 2.

Another chord is AP: using its endpoints, I found its midpoint and its slope.

From these values, I could find the equation of its perpendicular bisector (not a lot of fun, for it had a lot of a-terms and square roots).

Then, I found the intersection of this perpendicular biscector with the line x = -7 and the intersection of this perpendicular bisector with the line x = 2 (there were still a lot of a-terms and square roots).

With these two points (the centers of the circumcircles), I could find the distance from one center to point P and the distance from the other center to point P (By this time, I was on a firt-name basis with the a-terms and square roots).

Since these are equal, by solving this equation, I could find the value of a, which was -14.

This is the x-value of point A, allowing me to find the y-value of point A, 15, which is the height of triangle ABC.

With the height 14 + 8 = 22 and the base 15, the area is 165.

Guest May 30, 2020