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# 2 concentric circular regions have radii of 1 inch and 10 inches. The rest of the question is down below...?

What is the area, in square inches, outside the smaller region, but inside the larger region? Express your answer in a terms of "pie"

Please show work

### 3 Answers

- 1 decade agoFavorite Answer
It's not "pie." It's spelled pi, and it looks like this: π

We want the whole thing (everything inside the 10-inch radius), minus the smaller circle. Each circle has area A = π r², so:

π (10)² - π (1)² = 99π in²

- OwlwingsLv 71 decade ago
π is pronounced 'pie' but spelled as 'pi'. It is actually the Greek letter 'p' (don't ask me why!)

The area of a circle = π*r²

The area of the smaller circle is therefore π*1² = π*1

The area of the larger circle is π*10² = π*100

The area inside the circumference of the larger circle but excluding the area of the smaller circle is the difference between the two, therefore the area is equal to:

π*100 - π*1 = π*(100 - 1) = π*99 square inches

- 1 decade ago
r1 = 1

r2 = 10

area1 = PI*r1^2

area2 = PI*r2^2

area(diff) = area2 - area1

= (PI * r2^2) - (PI * r1^2)

= (r2^2 - r1^2) * PI

= 99 * PI