3 . Consider a circle with centre O and radius r cm. Triangle ABC is drawn such that its vertices are on the circumference of the circle . It is given that BC � 20 cm , ABC ˆ � 0.88 radians and ACB ˆ � 1.23 radians .
A
C O
B
( a ) Find AB .
( b ) Show that r
2
2
AB
� . 2( 1� cos A OB ˆ )
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