The arc length is
[tex]S=\displaystyle\int_C\mathrm ds[/tex]
where C is the given curve and ds is the line element. C is defined on 0 ≤ t ≤ 3π by the vector function,
[tex]\mathbf r(t)=(t\cos t,t\sin t)[/tex]
so the line element is
[tex]\mathrm ds=\left\|\dfrac{\mathrm d\mathbf r(t)}{\mathrm dt}\right\|\,\mathrm dt[/tex]
[tex]\mathrm ds=\sqrt{\left(\dfrac{\mathrm d(t\cos t)}{\mathrm dt}\right)^2+\left(\dfrac{\mathrm d(t\sin t)}{\mathrm dt}\right)^2}\,\mathrm dt[/tex]
[tex]\mathrm ds=\sqrt{1+t^2}\,\mathrm dt[/tex]
So we have
[tex]S=\displaystyle\int_0^{3\pi}\sqrt{1+t^2}\,\mathrm dt\approx46.132[/tex]
