## stupidinmath one year ago ---

1. Starr_DynastyT

@shamil98

2. stupidinmath

A= big semicircle.. what's next?

3. MayankD

50pi

4. MayankD

Just remove the semicircle on the left and place it in the gap on the right

5. oldrin.bataku

this is SAT yes? I remember this one

6. Haleo

$a= \pi*r ^{2}$ $a= ( \pi * 10^{2} ) /2 = 157.079$

7. Haleo

Isn't it right?

8. oldrin.bataku

|dw:1389510061781:dw|

9. oldrin.bataku

|dw:1389510085539:dw|

10. oldrin.bataku

|dw:1389510103621:dw| so the area is equivalent to just the top semicircle... we merely moved the piece under the line to fill the hole to the right

11. oldrin.bataku

the radius is very clearly $$r=10$$ ergo the area is $$A=\pi r^2=\pi(10)^2=100\pi$$

12. oldrin.bataku

|dw:1389510292746:dw|

13. liliegirl

It is a semicircle so you need to divide by 2. The answer is 50pi + 25pi over 2. $\frac{ 75\pi }{ 2 }$ is the answer.

14. oldrin.bataku

oops -- good catch. you do need to multiply by $$1/2$$ to get just the top:$$\frac12\cdot100\pi=50\pi$$that being said, it is NOT $$\frac12(50\pi+25\pi)$$

15. liliegirl

|dw:1389510798177:dw|

16. stupidinmath

so.. also find that part and add it?

17. liliegirl

You need to add that because it is also shaded. The area of that part is 25pi over two.

18. oldrin.bataku

@liliegirl that part is precisely the part we moved to fill in the top semicircle. it is now accounted for...

19. stupidinmath

oh. right

20. stupidinmath

so.. the answer is.. 314.16 right? thanks guys

21. liliegirl

@oldrin.bataku Ahhh, Sorry, I didn't notice.... :)))

22. oldrin.bataku

@stupidinmath no it's half of that, i.e. $$50\pi$$

23. stupidinmath

oh.. since its a semi circle.. k thanks :)