## stupidinmath one year ago ---

1. ganeshie8

you have two arcs of radius 10

2. ganeshie8

each arc is measuring exactly 1/4th of circle (why ?)

3. ganeshie8

so you can calculate the perimeter of shaded region ?

4. stupidinmath

so.. if i get the arc measures.. i'll just add both then i can already have the perimeter?

5. Andras

Do you know what is the perimeter of a full circle? If you do you can find the shaded one. As that is twice the quarter of a circle. Thus 2*1/4=1/2 The perimeter is half of the full circle. (with radius=10)

6. stupidinmath

my answer is.. P=900, is it correct?

7. Andras

Seems wrong. $\pi$ Is missing for sure.

8. Andras

What is the perimeter of a circle with radius=r?

9. stupidinmath

15.71 ?

10. stupidinmath

62.83

11. Andras

Do not try to jump steps. One at a time, otherwise you will make too many mistakes. So we will start with a circle of any radius=r. This circle has perimeter: $P=2\pi r$ Is this clear?

12. stupidinmath

yep, perimeter's 62.83 approximately

13. Andras

If r=10 as in this question. Now next step, first look at one arc of the graph. (half the perimeter asked) What fraction is this arc of the full circle?

14. stupidinmath

1/4 of the circle

15. Andras

Correct, thus one arc has perimeter: $\frac{ 1 }{ 4 } 2\pi r$

16. Andras

We need two arcs, so need to multiply the above equation by 2. $2*\frac{ 1 }{ 4 } 2\pi r =\pi r$

17. Andras

$solution: P=10\pi$

18. stupidinmath

15.71.. so.. 31.42 :)

19. stupidinmath

did i get it right?

20. Andras

Yes but I am 100% confident that your maths teacher will not like the solution written as 31.42, as it is not precise. The solution is $10 \pi$

21. stupidinmath

Hahah, yeah maybe. Alright. Got that. Thank you sooo much:)

22. Kainui

@Andras Don't be so sure. Often times in courses like this the teacher prefers that you assume pi=3.14, which is probably exactly what his teacher expects since he's already doing it this way.

23. Andras

You might be right but that hurts my soul :(