If the roots of the given equation (m2+1)x2+2amx+a2-b2=0 be equal, then
a2+b2(m2+1)=0
b2+a2(m2+1)=0
a2-b2(m2+1)=0
b2-a2(m2+1)=0
Roots are equal, then B2-4 AC=0
⇒4a2m2=4(m2+1)(a2-b2)
⇒a2-b2(m2+1)=0.