5 . Consider the following circle with centre O and radius r .
A C
The points A , B and C are on the circumference such that π
0 ��
� . 2
AOB ˆ � 2� ,
( a ) Show that AB �r 2 ( 1� cos 2 �)
.
Let P be the perimeter of the shaded region .
( b ) Show that P�2 r( �� sin �) .
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