Answer:
a. 29.3 units²
Explanation:
The area of a circle is A = πr².
The area of each triangle is A = ½bh.
The vertex angle of each triangle is 360/5 = 72°. If we cut the triangle in half, we can use trig to write:
sin 36° = (½b) / r
b = 2r sin 36°
And:
cos 36° = h / r
h = r cos 36°
Substituting, we get the area of each triangle is:
A = r² sin 36° cos 36°
A = ½ r² sin 72°
The radius of the circle is 8. So the area of the circle minus the area of the 5 triangles is:
A = π (8)² − 5 (½) (8)² (sin 72°)
A ≈ 48.9 units²
Three fifths of the area is shaded, so:
⅗ A ≈ 29.3