Having a bit of trouble with this one. Can anyone help me out?

Many thanks.C is a circle with centre (-1, -4). The midpoint of a chord of length $\displaystyle 2\sqrt{5}$ is (2, 0). Find the length of the radius of C.

Q.

Attempt:Perpendicular distance [bc] from centre c to x-axis is 4,

Let |ab| = 1/2 length of chord on x-axis = $\displaystyle \sqrt{5}$,

$\displaystyle |ac|^2=(\sqrt{5})^2+4^2=21\rightarrow |ac|=\sqrt{21}=$ radius,

(From text book): Radius = $\displaystyle \sqrt{30}$

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