Question 168637
{{{drawing( 400, 300, -45, 45, -45, 45,

  locate(0,0,o(A)),
  circle( 0,0, 20 ), 
locate(14,-18,(C)),
line(0,0,14,-18),
locate(0,-18,(B)),
line(0,0,0,-18),
triangle( 14,-18,-14,-18,0,27))}}}

AC is equal to the radius 20. 
We know that angle C is half of the original angle of the original equilateral triangle(60) ....so C is 60/2=30.   ABC is a right triangle so we know that angle A is a 60 degree angle  180-90-30=60
:
BC is equal to 1/2 of the entire side of the equilateral triangle 

and we know that sine 60 degrees =BC/20(hypothenuse of the ABC)--->solving for BC=20(sine60degrees)=17.32
:
now if we double BC we will have the entire length of one side of the equilateral triangle ( 17.32(2)=34.64)---> and since all sides are equal the Perimeter is three times this length. 34.64(3)=103.92 inches