Let and \( \det(A-aI)=0 \), where \( a \) is a real number. If the largest possible value of \( a \) is \( p \), then the circle \( (x-p)^2+(y-2p)^2=320 \), intersects the co-ordinate axes at:
\( 1 \) point
\( 2 \) points
\( 3 \) points
\( 4 \) points