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# Cheeky c2 question, I wonder who'll get it?? watch

1. (Original post by notnek)
You can take away the areas in red. But what are these areas?

They're not sectors...
Got it... finally. Feel so dumb now... thanks for the help
2. (Original post by AG98)
I'm probably being extremely dumb here, so sorry for that

But I still don't get why you can't just get the area of half the circle and take away the areas outlined in red here:

I understand that you could work out the area of the triangle OCB and take away the unshaded segments, but that just seems like a more complicated way of doing it, and while it does work, I still don't understand why the original way I did it was wrong
Look at the diagram, AOB is not a sector because it has two curved edges; you've assumed that the edge OB is straight rather than curved, so you missed the two little segments.
3. (Original post by AG98)
I'm probably being extremely dumb here, so sorry for that

But I still don't get why you can't just get the area of half the circle and take away the areas outlined in red here:

I understand that you could work out the area of the triangle OCB and take away the unshaded segments, but that just seems like a more complicated way of doing it, and while it does work, I still don't understand why the original way I did it was wrong
You need to find the area of the semi circle (1/2 x pi x r^2)

Find the area of the segment (RED) ((pi/3)/2pi x pi x r^2) - (1/2 x r^2 x sin(pi/3))

Find the area of the sector (BLUE) ((pi/3)/2pi x pi x r^2)

Then assemble this so you take away 2 sectors and 2 segments from the area of the semi circle. Then you expand everything and factorize, if you want to see clarification of this method scroll up to my working out.

Attached Images

4. (Original post by Louisb19)

x
+1 for those sick drawing skillz
5. (Original post by lizard54142)
+1 for those sick drawing skillz
Paint DD
6. (Original post by lizard54142)
+1 for those sick drawing skillz
Paint >

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