In a math activity class, Mr. Li led the students to measure the height of the teaching building. In the sunlight, the shadow length Ba of Huang Li's BC, who is 1.65 meters tall, is 1.1 meters. At the same time, the shadow length DF of the teaching building De is 12.1 meters. (1) please draw the projection DF of the teaching building de in the sunlight. (2) please calculate the height of the teaching building de according to the measured data (accurate to 0.1M)

In a math activity class, Mr. Li led the students to measure the height of the teaching building. In the sunlight, the shadow length Ba of Huang Li's BC, who is 1.65 meters tall, is 1.1 meters. At the same time, the shadow length DF of the teaching building De is 12.1 meters. (1) please draw the projection DF of the teaching building de in the sunlight. (2) please calculate the height of the teaching building de according to the measured data (accurate to 0.1M)

(1) (2) from the parallel projection, △ ABC ∽ FDE, bcba = dedf, ∽ de = BC · dfba = 1.65 × 12.11.1 ≈ 18.2 (m), that is, the height of the teaching building is about 18.2m

When measuring the height of an object, we often use the relationship between the shadow length and the height of the object at a certain time in the sun to calculate, always at the same time
The height of a place is in direct proportion to its shadow length. If the height of a bamboo pole is 1.5 meters at a certain time, its shadow length is 2.5 meters
(1) Write out the relation between the height h and the shadow length L at the same place at that time
(2) The height of flagpole with shadow length of 30 meters at the same place at that time can be calculated by using the relation

1、H/L=1.5/2.5=3/5
2. When the shadow is 30 meters long,
H / 30 = 3 / 5 -- > H = 18m

To build a cuboid uncovered pool with a volume of 16 cubic meters and a depth of 4 meters, if the cost of the pool bottom is 110 yuan per square meter and the cost of the pool wall is 90 yuan per square meter, what is the length of the cuboid______ The width is______ The cost of the pool is the lowest, and the lowest cost is______ ．

Suppose the length of the cuboid is XM, the width is YM, and the cost of the tank is s yuan. Then 4xy = 16, s = 110xy + 90 (8x + 8y).. s = 440 + 720 (x + y) ≥ 440 + 720 × 2XY = 3320, if and only if x = y = 2, take the equal sign. So the answers are: 2m, 2m, 3320 yuan

It is said that the shadow length of the tower is 23.5. What is the relationship between the shadow length and the elevation angle of the noon sun?

There is a negative correlation between shadow length and midday sun height angle, that is, the larger the midday sun height angle is, the shorter the shadow length is; on the contrary, the smaller the midday sun height angle is, the longer the shadow length is

As shown in the figure, the height of street lamp a is 7 meters, and there is a wall CD, CD ⊥ BD, 20 meters away from point B directly below the street lamp. If a student EF with a height of 1.6 meters stands on line BD (EF ⊥ BD, F, EF < CD), the total length of his shadow is 3 meters, and the distance BF from the student to point B directly below the street lamp is calculated

Let the distance BF from the student to point B directly below the street lamp be x meters. (1) when all the shadows are on the ground, the shadow length FG = 3 meters ⊥ ab ⊥ BD, EF ⊥ BD ⊥ fgbg = efab, ⊥ 3x + 3 = 1.67, and the solution is x = 818 = 10.125 meters. X + 3 = 13.125 ⊥ 20

As shown in the figure, an isosceles trapezoid flowerbed should be designed. The upper bottom of the flowerbed is 120 meters long, the lower bottom is 180 meters long, and the distance between the upper and lower bottom is 80 meters. There is a transverse channel at the connecting line (dotted line) between the middle points of the two waists. There are two longitudinal channels between the upper and lower bottom, and the width of each channel is equal. Let the width of the channel be x meters (1) (2) when the area of the three passageways is one eighth of the trapezoidal area, the width of the passageway shall be calculated; (3) according to the design requirements, the width of the passageway shall not exceed 8 meters. If the total cost of building the passageway (10000 yuan) is in direct proportion to the width of the passageway, the proportion coefficient is 5.5, and the greening cost of the rest of the flower bed is per square meter When the width of the passage is 0.02 million yuan, the total cost of the flower bed is the least? How much is the minimum cost?

(1) The area of the transverse corridor is: (120 + 180) △ 2 × x = 150x (M2); (2) according to the meaning of the title: 2 × 80 × x + 150x-2x2 = 18 × (120 + 180) △ 2 × 80, it is sorted out: x2-155x + 750 = 0, X1 = 5, X2 = 150 (not in line with the meaning of the title, omit), so the width of the corridor is 5m; (3) the total cost of building flower beds is y 10000 yuan, then y = 0.02 × [(120 + 180) △ 2 × 80 - (- 2x2 + 310x)] + 5.5x, = 0.04x2-0 7x + 240, when x = - B2A = 8.75, the value of Y is the minimum. ∵ according to the design requirements, the width of the corridor should not exceed 8m, ∵ when x = 8m, the total cost is the least, that is, the minimum cost is 0.04 × 82-0.7 × 8 + 240 = 2.3996 million yuan

As shown in the figure, for a rectangular piece of paper ABCD, its length ad is a and width AB is B (a > b). Select a point m on the edge of BC and fold △ ABM along am from B to B '. If B' is the symmetry center of rectangular piece of paper ABCD, then the value of AB is___ ．

Because B 'is the center of symmetry of the rectangular paper ABCD, ab' C is the diagonal of the rectangle. According to the properties of folding, AC = 2Ab ′ = 2Ab = 2B, ﹥ sin ∠ ACB = AB: AC = 1:2, ﹥ ACB = 30 °, cos ∠ ACB = cos30 ° = a: B = 3

Mathematical expression of bulk expansion coefficient
Explain what each component represents. For example, t stands for time
Don't high school messy don't understand. Is the most basic kind

Bulk expansion coefficient β = △ V / △ t
β - bulk expansion coefficient: the increment of unit volume when the temperature rises by 1 ℃
Delta V: volume change
Δ T: temperature change (1 ℃)

Why is the proportional coefficient 1 in the mathematical expression of Newton's second law
Through the experiment, we can only prove that f is proportional to Ma, but why is the proportional coefficient directly taken as 1 in the calculation? Can we specifically prove that f = ma?

LZ reverses the causality. We can only say that f is directly proportional to ma. For convenience, we will position the proportion coefficient in the international system of units as 1, but this is only in the international system of units. If it is not for this system of units, the proportion coefficient will not be 1. The specific can be obtained by comparing with the international system of units
We define it like this, so it's meaningless to talk about proof

Mathematical software for calculating variable expression
I need a mathematical software that can sort out the relationship between variables
such as
a/b+x^2+7*y^3=b
Then we find the relation between X and y, and the result is similar to y = f (x)

Mathematica
Symbolic computing is very powerful, which is better than MATLAB and maple in the field of symbolic computing
As you said, this equation can be solved