The centre of the circle C1 will be (2,0) and radius is 2
So, the equation of the circle C1 is x2+y2−4x=0
Let θ be the angle made by the line y=2x with positive x-axis.
i.e. tanθ=2

Now C2 is a circle with OA as diameter.
So, tangent at A on C2 is perpendicular to OA
Let OA=l

∴APQA=ltanθlcotθ
⇒APQA=tan2θ1=41