Let A, B be points on the two half-lines x- 3 |y|= , >0 at a distance of from their point of intersection P. The line segment AB meets the angle bisector of the given half-lines at the point Q. If PQ= 92 and R is the radius of the circumcircle of PAB, then 2R is equal to .
Answer
9
Solution
[figure]
x- 3 |y|= y= x- 3, x : two half-lines from P( , 0)
Slopes 1 3 each makes 30 with the x-axis =60
PA=PB= and =60 PAB is equilateral with side
The bisector (x-axis) meets AB at its mid-point Q, so PQ is the altitude:
PQ= 32 = 92 =3 3
Circumradius of an equilateral triangle: R= 3=3
2R= 273=9
Answer: 9