Question

A circular question which I do not understand.
I have found out the area of OAB and OAC but am not sure what to do next.
http://i.imgur.com/rwz7sfW.png

Answer 1

How have you determined the area of OAB?

Answer 2

OAB=36theta
OAC=8pi

Answer 3

what doesnt make sense in my mind is how if OAC is a semicircle... how does length OA = OB...?

Answer 4

ie a circle should be widest at it's midpoint
line OA = diameter
so line OB cant equal diamater
line OB < diameter...?

Answer 5

this isn't making logical sense to me @thomaster and @ganeshie8 ... any ideas...?

Answer 6

duh, idiot jack, disregard, OAB is a sector of a different circle, not the same circle, my bad

Answer 7

Area of Sector =
\[A1 = \frac{ 1 }{ 2 } \times r^2 \times \alpha (inradians)\]
Area of a semicircle =
\[A2 = \frac{ 1 }{ 2 } \times pi \times r^2\]

A1 x 2 = A2
so :
[\[2 \times A1 = r^2 \times \alpha (inradians) = \frac{ 1 }{ 2 } \times pi \times r^2\]

Answer 8

can you solve from here @williamnz ?

Answer 9

@williamnz just a note: the A1 x 2 = A2
comes from the question itself:
"the area of semicircle OAC is twice the area of sector OAB"
also, my mistake earlier was assuming it was all part of the one circle
its more like:

Answer 10

Hi @Jack1 thanks for the help, the reason I didn't understand it is because I put the wrong numbers into the equation -.-