Mass per unit area of a circular disc of radius a depends on the distance r from its centre as σ(r)=A+Br The moment of inertia of the disc about the axis, perpendicular to the plane and passing through its centre is :
A.2πa⁴(A/4+aB/5)
B.2πa⁴(aA/4+B/5)
C.πa⁴(A/4+aB/5)
D.2πa⁴(A4+B/5)