If 3x2+2λxy+3y2+(6−λ)x+(2λ−6)y−21=0 is the equation of a circle, then its radius is

We have,3x2+2λxy+3y2+(6−λ)x+(2λ−6)y−21=0…(i)This equation will represent a circle, ifCoeff. of xy=0⇒λ=0Putting λ=0 in (i), we obtain x2+y2+2x−2y−7=0Clearly, it represents a circle of radius =1+1+7=3.