## El_Arrow one year ago stuck in arc length problem

1. El_Arrow

2. El_Arrow

@freckles

3. El_Arrow

how does it get the 2650/4 + 441x/4?

4. El_Arrow

im getting 1325/2 on my calculator

5. anonymous

|dw:1434600730609:dw|

6. anonymous

2650/4=1325/2

7. El_Arrow

but then why didnt the person put 1325/2 in the problem?

8. anonymous

it looks like they wanted to pull the 1/4 out from under the radical.

9. El_Arrow

oh i see

10. El_Arrow

one more thing

11. El_Arrow

what did he do here?

12. El_Arrow

like how did he get the 3+y=(1/8)tangent(theta)?

13. anonymous

that's a trig substitution from right angle trig. basically if you have an integral of the form $\sqrt{b^2+a^2x^2}$you can make the substitution x = (a/b) tan Θ

14. anonymous

I reversed that. x = (b/a) tan Θ

15. El_Arrow

so the x is (3+y), the b is 1 and a is 8? right?

16. anonymous

yes

17. El_Arrow

okay thanks

18. anonymous

you're welcome