Answer:
S(a) = 27,5036 squared units
Step-by-step explanation:
Shaded area is :
S(a) = Area of the circle - area of the regular pentagon (1)
A(c) = area of the circle
A(c) = π*(r)² ⇒ A(c) = π*(6)² ⇒ A(c) = 36*π ⇒ A(c) = 113,0976 squared units
Area of a regular pentagon:
a) If we draw a straight line between the center and each vertex we get 5 triangles, and if we draw the apothem for each side, we get 10 triangles. We will calculate the area of one of these triangles
The first 5 triangles has a central angle equal to 72⁰ according to:
360/5 = 72
When we divide these triangles in two triangles by means of the apothem, each central angle will be of 36⁰, then
sin 36⁰ = 0,58778 and cos 36⁰ = 0,809017 and sin 36⁰ = x/6 here x is half of the side of the regular pentagon. Then
0,58778 = x/6
x = 6*0,58778
x = 3,52668 units of length
and cos 36⁰ = a/6 where a is the apothem, then
0,809017 = a / 6 ⇒ a = 6*0,809017
a = 4,8541 units of length
Now we are in conditon to calculate area of the triangles as:
A(t) = (1/2)*b*h
A(t) = (1/2)*x*a ⇒ A(t) = 0,5* 3,52668*4,8541
A(t) = 8,5594 squared units
Finally we have 10 of these triangles, then
Area of regular pentagon is : 10*A(t) squared units
A(p) = 85,594 squared units
Now plugging these values in equation (1) we get the shaded area
S(a) = 113,0976 - 85,594
S(a) = 27,5036 squared units
