The diagram depicts a circle with centre $O$, and $AC$ and $BD$ are diameters.
(a)[3]
Show that triangle $OAB$ is congruent to triangle $ODC$.
Give a reason for every statement that you make.
(b)[5]
The circle has a diameter of $10\text{ cm}$ and $AB = 9\text{ cm}$.
Calculate the difference between the circumference of the circle and the perimeter of the shaded shape.
Worked solution & mark scheme
This 8-mark question has a full step-by-step worked solution and mark scheme. One marking point: “$AO=DO$, $BO=CO$, $\angle AOB=\angle DOC$, so SAS applies” …