1. The problem statement, all variables and given/known data If the pair of lines x^2-2pxy-y^2=0 and x^2-2qxy-y^2=0 are such that each pair bisects the angle between the other pair, then what is the value of pq? 2. Relevant equations 3. The attempt at a solution I don't understand what 'each pair bisects the angle between the other pair' mean. Is it that each line of first pair bisects the angle between the two lines of other pair (obtuse and acute angle)?. How do I proceed with this question?