The point A has coordinates $\displaystyle (2, -1)$. Find the equation of the chord of the circle which has $\displaystyle A$ as its midpoint.

I don't know how to do it with limited information. Could somebody help please? I'm a bit shoddy at these questions.

It has preceding questions which say let $\displaystyle C$ be the circle with equation $\displaystyle x^2 + y^2 - 2x + 4y - 11 = 0 $

I found the centre and radius.

Then it asked me to determine whether the origin lies inside or outside C; it lies inside.