# Math Help - length of arc of circle

1. ## length of arc of circle

In the figure above, if the radius of the circle is 8, and triangle TRS is inscribed in the circle, then the length of arc TRS is
A.
16π/3

B.
(32 π)/3

C.
16 π

D.
(128 π)/3

E.
64 π

2. Originally Posted by mths

In the figure above, if the radius of the circle is 8, and triangle TRS is inscribed in the circle, then the length of arc TRS is
A.
16π/3

B.
(32 π)/3

C.
16 π

D.
(128 π)/3

E.
64 π

Since the triangle is equilateral (all interior angles are equal) the arc in question is $\frac23$ of the complete circumference of the circle:

$a = \frac23 \cdot 2\pi \cdot 8$