The combined equation of the lines l1,l2 is 2x2+6xy+y2=0 and that of the lines m1,m2 is 4x2+18xy+y2=0. If the angle between l1 and m2 is α the angle between l2 and m1 will be

The combined equation of bisectors of angle between the lines of first pair and second pair are same which is 3(x2−y2)=(2−1)xytherefore two pairs are equally inclined to each other