MathDB
Chord Through Two Circles

Source:

December 30, 2006
geometryrectangletrigonometryrotationAMCAIMEinequalities

Problem Statement

In the adjoining figure, two circles of radii 6 and 8 are drawn with their centers 12 units apart. At PP, one of the points of intersection, a line is drawn in such a way that the chords QPQP and PRPR have equal length. Find the square of the length of QPQP.
[asy]unitsize(2.5mm); defaultpen(linewidth(.8pt)+fontsize(12pt)); dotfactor=3;
pair O1=(0,0), O2=(12,0); path C1=Circle(O1,8), C2=Circle(O2,6); pair P=intersectionpoints(C1,C2)[0]; path C3=Circle(P,sqrt(130)); pair Q=intersectionpoints(C3,C1)[0]; pair R=intersectionpoints(C3,C2)[1];
draw(C1); draw(C2); //draw(O2--O1); //dot(O1); //dot(O2); draw(Q--R);
label("QQ",Q,N); label("PP",P,dir(80)); label("RR",R,E); //label("12",waypoint(O1--O2,0.4),S);[/asy]