If the pair of lines x2+2xy+ay2=0 and ax2+2xy+y2=0 have exactly one line in common, then a=

Let y=mx be a line common to the given pairs ofam2+2m+1=0 and m2+2m+a=0∴ m22(a−1)=m1−a2=12(a−1)⇒ m2=1 and m=−a+12⇒ (a+1)2=4⇒a2+2a−3=0⇒a=−3,1But, for a=1, the two pairs have both the lines common.Hence, a=-3.