# Arc length of circle

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1. Oct 18, 2015

• Member warned about posting with no effort shown
1. The problem statement, all variables and given/known data
find the arc length of a circle in the first quadrant with an equation x2 + y2 = a2

2. Relevant equations
arc length = ∫ √(1 + (dy/dx)2) dx

3. The attempt at a solution
i got stuck on how to solve the integral

2. Oct 18, 2015

### SteamKing

Staff Emeritus
Well, show us where you got stuck.

Did you calculate dy/dx for the arc of the circle, using its equation?

3. Oct 18, 2015

yeah, i make the circle equation into y= √(a2-x2) , and then put it into the arc length equation.
the problem is i cant solve my integral equation.

4. Oct 18, 2015

### Staff: Mentor

You still didn't show the integral you want to solve and how you got it.

Did you try the usual trigonometric substitutions?

5. Oct 18, 2015

first i derive my y=√(a2-x2) into y'= - x/√(a2-x2)
and then put it into arc length equation = ∫ √(1+(dy/dx)2) dx
resulting ∫ √(1+(- x/√(a2-x2))2) dx
and i got stuck there. i dont know how to solve my equation, and i didnt use trigonometric substitution

6. Oct 18, 2015

### Staff: Mentor

Then you should try that (after simplifying the expression a bit).