In a triangle PQR, PS is the angle bisector of angle QPR and angle QPS = 60 degrees. What is the length of PS?
A. (q+r)^2 / (qr)
B. qr / (q+r)
C. sqrt(q^2 + r^2)
D. (q+r) / (2qr)
GATE 2015 · General Aptitude · Triangles · hard
Answer: PS = qr / (q + r)
State the angle bisector length formula: Let PQ = r, PR = q, half-angle = 60 degrees. Then PS = (2qr / (q+r)) * cos(60).