As shown in Figure 6, for a piece of land, ∠ ADC = 90 °, ad = 12M, CD = 9m, ab = 39m, BC = 36, calculate the area of this land Seeking process

Connect AC
In right angle delta ADC
AC=√AD² +DC² =√12² +9² =15
Because AC & # 178; = 225, BC & # 178; = 36 & # 178; = 1296, AB & # 178; = 39 & # 178; = 1251
So AC & # 178; + BC & # 178; = AB & # 178;
So △ ABC is a right triangle, and ∠ B = 90 degrees
So the area of this land = s △ ADC + s △ ABC = 1 / 2 * 12 * 9 + 1 / 2 * 15 * 36 = 54 + 270 = 324

It is planned that 15 people can move a pile of bricks in 4 hours. After 2 hours of actual labor, 5 people will be transferred. How many hours will it take to move the remaining bricks

(1-14 × 2) / [115 × 14 × (15-5)] = (1-12) / [160 × 10], = 12 ／ 16, = 3 (hours); answer: it will take 3 hours to move the remaining bricks

Junior high school mathematics calculation problem, mathematical genius come quickly
5+5^2+5^3+… +5^n
1+(1/1+2)+(1/1+2+3)+… +(1/1+2+… +100)
200420032003+200520042004-200320042004-200420052005
When n is infinite, 1 + (1 / 2) + (1 / 4) + (1 / 8) + +(1 / 2 ^ n)
Natural numbers are arranged in the following table according to certain rules. What is the fifth number in line 200?
one
2 3
4 5 6
7 8 9 10
………………
To solve this problem, there is 1 ^ 2 in the formula, which means the second power of 1

(1) Original formula = (5-1) * (1 + 5 + 5 ^ 2 + 5 ^ 3 +...) +5 ^ n) / (5-1) - 1 = (5 ^ (n + 1) - 1) / 4-1 (2) the general formula is: 2 / (n * (n + 1)) = (1 / n-1 / (n + 1)) * 2, so the original formula = 2 (1-1 / 2 + 1 / 2-1 / 3 + 1 / 3-1 / 4 + 1 / 4-1 / 5. - 1 / 100 + 1 / 100-1 / 101) = 2 (1-1 / 101) = 200 / 101; (3) the original formula = 2004 * 2003 * 10

The area of a square and a circle is 2 square centimeters. Which of them has a larger perimeter?
Please explain by calculation

If the side length of a square is 2T cm under the root sign, the perimeter is
4 * 2tt under root = 32tt under root
The square of circle area TTR = 2tt r = root 2
Perimeter = 2 * TT * root 2 = 2 root 2 * TT = square of 8 * TT under root
The perimeter of a square is greater than that of a circle

a. B is a rational number, and | a + B | = A-B, try to find ab

∵a + B | = a + B or - A-B, ∵ a + B = A-B or - A-B = A-B, the solution is b = 0 or a = 0, ∵ AB = 0

Help me solve these problems, please
1. The route from city a to city B is 1200 km long. It takes 2 hours and 30 minutes for an aircraft to fly from city a downwind to city B, and 3 hours and 20 minutes for an aircraft to fly from city B upwind to city B. the average speed and wind speed of the aircraft can be calculated
2. Each tin sheet can be made into 25 tin bodies or 40 tin bottoms. One tin body and two tin bottoms form a set of tin. There are 36 tin sheets. How many tin bodies can be used and how many tin bottoms can make the tin body and the tin bottom match each other?
In addition, we need to solve the problem with binary linear equation and have a detailed process

Suppose the average speed is x km / h and the wind speed is y km / h
2.5(X+Y)=1200,
two hundred
￣(X-Y)=1200;
sixty
The solution is: x = 420, y = 60
The box body is made of X sheets and the bottom is made of Y sheets
X+Y=36,2×25X=40Y
The solution is as follows
X=16,Y=20

The distance between two large and small squares is 1cm. If the area between two squares is 12 square, what is the area of large and small squares?
The ring with an area of 12 is divided into four small rectangles, each of which is 12 divided by 4 = 3 square centimeters;
The width of a small rectangle is 1 cm, and the length is 3 square centimeters divided by the width of 1 = 3 cm;
The area of a small square is 3cm - 1cm = 2cm, and the area is 2cm x 2cm = 4cm;
Large square area is 2 cm + 2 cm = 4 cm, area is 4 cm = 16 square cm
OK!

Let the side length of a small square be a,
Then: annular area = 4 * (1 * a) + 4 * 1 * 1 = 12 cm
A = 2 cm
Then the area of the small square is 2 * 2 = 4cm

How did scientists first measure the distance from the earth to the sun?
This problem has bothered me for a long time. Please do me a favor

The first one to measure the distance between the earth and the sun was eratosini of ancient Egypt. He first calculated the distance between the moon and the earth according to the observation of the eclipse and the earth's radius determined by himself earlier. Then by observing the phase of the moon, he knew that the crescent moon (exactly half of the moon) was the sun's light shining on the moon from the front side, Then the sun earth moon angle should be exactly 90 degrees. In fact, it was 89 degrees according to their measurement at that time. So this is a right triangle, There is a right angle to the moon (the sun shines from the front side). Here is 89 ° on the earth. The distance between the earth and the moon is known. According to the trigonometric relationship, the length of the hypotenuse of the earth and the sun can be calculated. Although this idea is really ingenious and beautiful, due to the limitation of the instrument conditions at that time, the measured result is very inaccurate (the angle is not 89 ° and should be closer to 90 °), This angle difference is a little bit, that distance difference is a lot). It is dozens of times different from what we know today! But after all, more than 2000 years ago, it was the first time that human beings measured the distance to the sun. It is still of great significance

It's better to have a process,
The outer wall of a civil building in the north is 240mm thick brick wall, with reinforced concrete ring beams and aseismic columns. The rooms are open at 3300mm, with height of 2700mm, windows of 1500*1500mm, polyurethane rigid foam (thickness of 40mm), external insulation, thermal conductivity of the materials used: brick wall: 0.81, reinforced concrete: 1.74, polyurethane rigid foam: 0.033, try to calculate the average heat transfer coefficient of the external wall.

The coefficient of thermal conductivity is only the thermal conductivity of materials, which has little to do with space, so the spatial data is not useful, but the coefficient of thermal conductivity of different materials is still useful
The thermal conductivity of three materials is converted according to the ratio of their thickness. You don't mention the thickness of brick wall and reinforced concrete, so it can't be calculated
If there is, for example, the existing data are 0.033 and 40mm, and the thermal conductivity is 0.0055

Take 30 cm square paper sheets and roll them into the largest cylinder. What are the bottom area, perimeter and height of the cylinder

Its bottom circumference is 30 cm and its height is 30 cm
Because the perimeter and height of the bottom are equal to the side length of the square

As shown in Figure 6, for a piece of land, ∠ ADC = 90 °, ad = 12M, CD = 9m, ab = 39m, BC = 36, calculate the area of this land Seeking process