Answer:
 Area = 11.66 square inches .
Explanation:
Given : An equilateral triangle (regular 3-gon) with the given measurement. 
3-inch radius.
To find : Find the area .
Solution : We have given that 
Radius = 3 inches.
By the formula : 
.
Plug the value of radius = 3 inches .
 
.
On multiplying both sides by 3.
 
.
On Dividing both sides by root 3 both sides .
 .
Side = 5. 19.
Area of equilateral triangle : 
.
Plug side = 5.19
Area of equilateral triangle : 
.
Area = 11.66 square inches .
Therefore, Area = 11.66 square inches .