A ring with an inner diameter of 5cm and an outer radius of 3cm. The area of the ring is______ cm2．

A ring with an inner diameter of 5cm and an outer radius of 3cm. The area of the ring is______ cm2．

5 △ 2 = 2.5 (CM) 3.14 × (32-2.52) = 3.14 × 2.75 = 8.635 (square cm). Answer: the area of this ring is 8.635 square cm. So the answer is: 8.635

How much is the area of a circle with a diameter of 5cm increased by 3cm?

The original radius is 5 △ 2 = 2.5cm
Now 2.5 + 3 = 5.5cm
So increase 3.14 × 5.5 × 5.5-3.14 × 2.5 × 2.5 = 75.36 square centimeter

If the radius of a circle is a centimeter and 2: a = A: 3, what is the area of the circle in square centimeter?

6pi

The radius of a circle is r cm long. How much is the area of the circle reduced by 2 cm?

π R & # 178; - π (R-2) &# 178; = π R & # 178; - π R & # 178; + 4 π R-4 π = 4 π (R-1) (square centimeter)