The formula of inclusion exclusion principle in primary school should not be too complicated

The formula of inclusion exclusion principle in primary school should not be too complicated

The core formula: (1) the inclusive and exclusive relation formula of two sets: a + B = a ∪ B + a ∩ B (2) the inclusive and exclusive relation formula of three sets: a + B + C = a ∪ B ∪ C + a ∩ B ∩ C + C ∩ A-A ∩ B ∩ C example 1: the total number of students in a class of a university in 2004 is 32, and there are 26 students in the first exam

The cross section of a steel pipe is annular, with an inner radius of 5cm and an outer diameter of 8cm. What is the cross section area of the steel pipe in square centimeter?

π (5 * 5-4 * 4) = 9 π = 28.26 (cm2)

The cross section of a steel pipe is annular, the radius of the inner circle is 5cm, and the area of the outer circle is 8cm?

Let the radius of the outer circle be r
So 3.14 * r * r - 3.14 * 5 * 5 = 8
Then the area of the outer circle = 8 + 3.14 * 5 * 5 = 86.5
The cross-sectional area is 86.5

The cross section of a steel pipe is annular. The diameter of the inner circle is 6cm, and the radius of the outer circle is 5cm?
There should be steps and reasons,

S = 3.14 * 5 * 5-3.14 * 3 * 3 = 50.24