(i)[2]
Determine the value of $\alpha$.
(ii)[3]
The area of the shaded region is given as $30\text{ cm}^2$. Determine the value of $r$.
Mathematics 9709 · AS & A Level · Circular measure
Circular measure — practice question
The diagram shows $OCA$ and $ODB$ as radii of a circle whose centre is $O$ and whose radius is $2r$ cm. $
ngle AOB = \alpha$ radians. $CD$ and $AB$ are arcs of circles with centre $O$ and radii $r$ cm and $2r$ cm respectively. The perimeter of the shaded region $ABDC$ equals $4.4r$ cm.