The image of the drumhead gives us the diameter of the circle which is 10 inches. This is the straight-line distance from one point of the circle through the center to the opposite point on the circle. We will first calculate the radius of the circle which is the straight-line distance from the center to a point on the circle which is equal to half the diameter:
R = D/2 = 10 in/2 = 5 in
The circumference of a circle is given by the equation C = πD where D is the diameter. Since π
is the number representing the ratio of the circumference to the diameter, multiplying the diameter by π will give us the circumference:
C = πD = π(10 in) = 10π in
We have given the exact value here in terms of π. If you must give an approximate answer, simply multiply 10 by 3.14:
C = 10π in ≈ 10×3.14 in = 31.4 in
The area of a circle is the space it takes up and is given by the equation A = πR2. Since we know the radius already, we can use this equation to calculate the circle's area:
A = π(5 in)2 = 25π in2
Again, if needed, the approximate value of this area is:
A = 25 π in2 ≈ 25 × 3.14 in2 = 78.5 in2