3

Part of 1981 Spain Mathematical Olympiad

Problems(1)

angle of intersecting lines wanted such that symmetric to be coplanar

Source: Spanish Mathematical Olympiad 1981 P3

Given the intersecting lines

r

s

, consider the lines

u

v

as such what: a)

u

is symmetric to

r

with respect to

s

v

is symmetric to

s

with respect to

r

. Determine the angle that the given lines must form such that

u

v

to be coplanar.

lines3D geometrygeometrysymmetry