The sum of the areas of two circles with a diameter of 10 cm is equal to that of a circle with a diameter of 20 cm______ ．

The sum of the areas of two circles with a diameter of 10 cm is equal to that of a circle with a diameter of 20 cm______ ．

The sum of the areas of two circles with a diameter of 10 cm: 3.14 × (10 △ 2) 2 × 2 = 157 (square centimeter), the area of a circle with a diameter of 20 cm: 3.14 × (20 △ 2) 2 = 314 (square centimeter), 157 square centimeter ＜ 314 square centimeter, so it is wrong that the sum of the areas of two circles with a diameter of 10 cm is equal to the area of a circle with a diameter of 20 cm

Is the area of a circle 40 cm in diameter equal to the sum of the areas of two circles 20 cm in diameter? Why
Don't make a list

Answer: not equal
Reason: the area of a circle with a diameter of 40 cm: 20 square times π, the result is 400 π square cm
The sum of the area of two circles with a diameter of 20cm: the square of 10 times π, and then multiplied by 2, the result is 200 π square centimeter
So it's not equal
The formula is not in the right format, so the text describes it

The area of a circle ten centimeters in diameter is equal to the sum of the areas of two circles five centimeters in diameter

Right

The outer diameter of a ring is 10 cm, and the inner diameter is 8 cm. What is its area?

3.14*（10*10-8*8）
=3.14*（100-64）
=3.14*36
=113.04 (cm2)