Area of circular ring: external circular area-internal circular area (πx long radius square -πx short radius square \πx (long radius square-short radius square).

Expressed in letters:

Within s+outside s (πR2)

External s- internal s = π (R2-R2)

Extended data

1, the area of a graph is equal to the sum of its parts;

2. The areas of two congruent figures are equal;

3. Triangles, parallelograms and trapezoids with equal bases and equal heights (equal-base trapezium should be understood as the sum of two bases) have equal areas;

4. The area ratio of equilateral triangle, parallelogram and trapezoid is equal to the corresponding height (or bottom) ratio;

5. The area ratio of similar triangles is equal to the square of the similarity ratio;

6. The ratio of the area of an equilateral or complementary triangle is equal to the ratio of the product of two sides of the equilateral or complementary triangle; The area ratio of equilateral parallelogram is equal to the ratio of the products of two equilateral sides;

7. Any curve can be expressed by a function y=f(x), so the area surrounded by this curve is to integrate x.