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The circumference of a semicircle is 25.7 decimeters, and the area of this semicircle is () square decimeters
The circumference of a semicircle is 25.7 decimeters, and the area of this semicircle is (157) square decimeters
Semicircle circumference = circle circumference ÷ 2 + diameter = 3.14 × Diameter ÷ 2 + diameter = (3.14 ÷ 2 + 1) × diameter
Therefore, diameter = 25.7 ÷ (3.14 ÷ 2 + 1) = 25.7 ÷ 2.57 = 10 (decimeter)
Area of semicircle = 3.14 × ten × 10 ÷ 2 = 157 (square decimeter)
The circumference of a circle is 31.4 decimeters. What is its area
31.4 = 2* 3.14 * r
r= 5
s= 3.14* 5*5
If the radius of the sector is 9dm and the arc length is 20dm, the sector area is () square decimeter?
If the radius of the sector is 9dm and the arc length is 20dm, the sector area is (1 / 2 * 9 * 20 = 90) square decimeters
It is known that the radius of a sector is 6, the center angle is 120 °, and the area and perimeter are calculated
The area is (120 × π × six ²） ÷360=12π
Perimeter is (120) × π × 6）÷180=4π
Judge whether △ ABC is an acute triangle, a right triangle or an obtuse triangle 1.a=5,b=12,c=13 2. Vertex coordinates a (6, - 7) B (7,5) C (2,3) 3. A = 2 b = root 2 C = root 3 + 1
1. Use Pythagorean theorem! 5 ^ 2 + 12 ^ 2 = 169 = 13 ^ 2 right triangle
2. Use vectors! Vector CA = (4, - 10), vector CB = (5,2), ca * CB = 20-20 = 0 right triangle
3. Use the cosine theorem! 4 + 2 - (root 3 + 1) ^ 2 = 2-2 root 3
Judge whether each acute triangle can be divided into right triangle and two obtuse triangles?
A: No
An acute triangle can be divided into two right triangles
However, it cannot be divided into two obtuse triangles:
The dividing line must pass through the vertex and the opposite edge, and the divided vertex angle is divided into two smaller acute angles,
The 180 ° edge line on the opposite side can only distinguish an obtuse angle and an acute angle at most,
Therefore, only one obtuse angle can be segmented at most, and two obtuse triangles cannot be segmented
RELATED INFORMATIONS
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- 14. The outer diameter of the train wheel is 0.8 meters. If it rotates 400 times per minute, how many kilometers does the train travel per hour
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