What is the condition for the lines xcosα+ysinα=p1x \cos \alpha + y \sin \alpha = p_1xcosα+ysinα=p1 and xcosβ+ysinβ=p2x \cos \beta + y \sin \beta = p_2xcosβ+ysinβ=p2 to be perpendicular?
α−β=π2\alpha - \beta = \frac{\pi}{2}α−β=2π
α=β\alpha = \betaα=β
α+β=0\alpha + \beta = 0α+β=0
α−β=π\alpha - \beta = \piα−β=π