Answer:
342.24 units²
Step-by-step explanation:
The area of one of the 8 triangular sections of the octagon is ...
A = (1/2)r²·sin(θ) . . . . . where θ is the central angle of the section
The area of the octagon is 8 times that, so is ...
A = 8·(1/2)·11²·sin(360°/8) = 242√2
A ≈ 342.24 units²
