State the range of possible values for $k$.

Given that $k=36$, write down the radius of $C$.

The circle $C$ has centre $A$ with coordinates $(7,5)$.

The line $l$, with equation $y=2x+1$, is the tangent to $C$ at the point $P$, as shown in Figure 3.

Show that an equation of the line $PA$ is $2y+x=17$.

Find an equation to the tangent of the circle at point $P$.