Step-by-step explanation:
the whole circle arc is
2×pi×r
the angle of the whole circle is simply
2×pi (= 360°)
our angle is a part of the full circle angle : the 3pi/10 th part of 2×pi
so, the arc length is
2×pi×r × 3×pi/10/(2×pi) = 2×pi×r × 3×pi/(20×pi) =
= pi×r × 3/10 = pi×3 × 3/10 =
= pi × 9/10