In the middle of a circular grassland with a girth of 25.12 meters and a flower bed with a radius of 2.5 meters, how many square meters of grassland are left?

Perimeter = 2 π * r = 25.12
So r = 4
Circular grassland area = π * r * r = π * 4 * 4 = 16 π
The area of flower bed with radius of 2.5m = π * 2.5 * 2.5 = 6.25 π
So the remaining grassland area is 16 π - 6.25 π = 9.75 π

A pool with a diameter of 10 meters is surrounded by a circular road with a width of 3 meters. How many square meters is the area of this road?

10 △ 2 = 5 (m), 5 + 3 = 8 (m), so the area of the path is: 3.14 × (82-52), = 3.14 × (64-25), = 3.14 × 39, = 122.46 (M2). A: the area of the path is 122.46 m2

How many square meters are left after a square flower bed with side length of 3 meters is built in the middle of a round grassland with radius of 5 meters

52 × 3.14-3 × 3, = 78.5-9, = 69.5 square meters. A: there are 69.5 square meters of grassland left

What is the sum of the faces of a triangle

Bottom area x height △ 2

Given the coordinates of the three vertices of a triangle, there are usually three methods to calculate the area of the triangle: Method 1: direct method. Calculate the length of one side of the triangle and find the height of the side; method 2: complement method. Convert the area of the triangle into the sum and difference of the area of several special quadrilateral and triangle; method 3: division method. Select an appropriate line to divide the triangle Cut it into two triangles which are easy to calculate the area. Now we give three coordinates: a (- 1,4), B (2,2), C (4, - 1). Please choose an appropriate method to calculate the area of △ ABC. Your answer is s △ ABC=______ ．

Through point a and point C, draw vertical lines to x-axis and y-axis respectively, and the two vertical lines intersect at point D. through point B, draw vertical lines to x-axis, and intersect CD at point e.. S △ ABC = s right angled trapezoid adeb + s △ bec-s △ ADC = (5 + 3) × 3 △ 2 + 2 × 3 △ 2-5 × 5 △ 2 = 52

A triangle, know the length of two sides, find the length of the third side. What is the relationship between the three sides? That is, the calculation formula
Any triangle can use the formula, urgent

Let two sides be a and B, and the third side be c
(1) If there are no other conditions,
You can know the range of the third edge. By using the sum of the two sides > the third edge, the difference between the two sides is less than the third edge
|a-b|

If the area and the length of two sides are known, how to calculate the length of the other side?

The angle between the two sides is a
The two sides are a, B
The other side is C
S=a*b*sinA/2
sinA=2S/ab
cosA=√(1-(2S/ab)^2)
c=√(a^2+b^2-2abcosA)
=√(a^2+b^2-2ab√(1-(2S/ab)^2))

Excuse me: if you only know the three sides of a triangle, can you find its area

Method 1
1. The three sides are set as a, B and C respectively, and the angles opposite them are set as a, B and C respectively
2. Cosine theorem: cosa = (B & # 178; + C & # 178; - A & # 178;) / (2 × B × C)
3、sinA=√（1-cos ²A）
4. Triangle area = B × C × Sina
Method 2
Suppose there is a triangle in the plane with side lengths a, B and C. the area s of the triangle can be obtained by the following formula:
　　S=√[p(p-a)(p-b)(p-c)]
In the formula, P is the half perimeter
　　p=(a+b+c)/2

Know two sides of a triangle and calculate the third side

Only know the length of both sides and the angle between them
For example, the length of both sides is a B and the angle is C
COSC = (a square + b square - C Square) / 2Ab
From this we can find the edge C
But at least in Shanghai, this is high school content

A right triangle knows an angle and how to calculate that angle

First, the sum of the internal angles of a triangle is 180 degrees
A right triangle must have an angle of 90 degrees
180-90-the known angle = another angle

In the middle of a circular grassland with a girth of 25.12 meters and a flower bed with a radius of 2.5 meters, how many square meters of grassland are left?