Finding arc length of a parametric curve

 
 
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Formula for arc length of a parametric curve

The arc length of a parametric curve over the interval ???\alpha\le{t}\le\beta??? is given by

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???L=\int^\beta_\alpha\sqrt{\left(\frac{dx}{dt}\right)^2+\left(\frac{dy}{dt}\right)^2}\ dt???

where ???\alpha??? and ???\beta??? are the limits of the interval

where ???dx/dt??? is the derivative of ???x(t)???

where ???dy/dt??? is the derivative of ???y(t)???

 
 

How to find the arc length of a parametric curve


 
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Calculating parametric arc length

Example

Find the length of the parametric curve over ???0\le{t}\le2\pi???.

???x=5\sin{t}???

???y=5\cos{t}???

We need to find the derivatives of the parametric equations.

???x=5\sin{t}???

???\frac{dx}{dt}=5\cos{t}???

and

???y=5\cos{t}???

???\frac{dy}{dt}=-5\sin{t}???

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Since we were given the limits of integration in the problem, we’re ready to plug everything into the arc length formula.

Since we were given the limits of integration in the problem, we’re ready to plug everything into the arc length formula.

???L=\int^{2\pi}_0\sqrt{(5\cos{t})^2+(-5\sin{t})^2}\ dt???

???L=\int^{2\pi}_0\sqrt{25\cos^2{t}+25\sin^2{t}}\ dt???

???L=\int^{2\pi}_0\sqrt{25(\cos^2{t}+\sin^2{t})}\ dt???

Since ???\cos^2{t}+\sin^2{t}=1???, we get

???L=\int^{2\pi}_0\sqrt{25(1)}\ dt???

???L=\int^{2\pi}_05\ dt???

???L=5t\big|^{2\pi}_0???

???L=5(2\pi)-5(0)???

???L=10\pi???

 
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