let A and B be d roots

thus A+B=a-2

AB=-a-1

A^2+B^2=(A+B)^2-2AB

solvin u get

A^2+B^2=a^2-2a+6=f(x)

this shud hav d least value  thus  f'(x)=0

thus

2a-2=0 thus a=1

@anchitsaini sorry ...ni dekha ki u posted d sol