If the pair of lines ax2+2(a+b)xy+by2=0 lie along diameters of a circle and divide the circle into four sectors such that the area of one of the sectors then

there are 4 sector let area of three sector is t each then area of bigger sector = 3t
total area = 6t so angle between these two lines will be 120 now apply fromula to finding angle between two lines for pair of lines