The distance between the pair of lines given by x2+y2+2xy−8ax−8ay−9a2=0, is

We have,     x2+y2+2xy−8ax−8ay−9a2=0⇒(x+y)2−8a(x+y)−9a2=0⇒(x+y−9a)(x+y+a)=0⇒x+y−9a=0,x+y+a=0Clearly, these lines are parallel. The distanced between these lines isd=|a−(−9a)|12+12=52a