On the roots of the quadratic equation (x + m) ^ 2 = n ^ 2 of X

(x+m)²=n²=(±n)²
x+m=±n
So x = - M-N, x = - M + n

Given that M is an integer, the quadratic equation mx2-2 (M + 1) x + m + 2 = 0 has two positive integer roots, then the value of M is

According to the root formula, we can get X1 = 1
x2=（m+2）/m=k
Then K is a positive integer m = 2 / (k-1)
When k = 2, M = 2; when k = 3, M = 1
Under other conditions, K is not a positive integer or m is not an integer
To sum up, M = 2 or M = 1

Given the quadratic equation x ^ 2-kx + K ^ 2-4 = 0 about X, and only one root of the equation is negative, find the value range of real number K

The equation has real roots and the discriminant is ≥ 0
(-k)^2-4(k^2-4)≥0
3k^2≤16
-4√3/3≤k≤4√3/3
Let two be X1 and X2 respectively
x1x2=k^2-4
If only one is negative, the other is 0 or positive
x1x2≤0
k^2-4≤0
k^2≤4
-2≤k≤2
In conclusion, - 2 ≤ K ≤ 2

If a hydrogen balloon floats in the air, should p take the density of air or the density of hydrogen to calculate the buoyancy

It should be air
You can think like this, what is the P of wood buoyancy in water? It's water! So this problem must be the density of air

It is known that the height of the triangular prism abc-a1b1c1 is 10 cm, and its bottom is an equilateral triangle with 4 cm side length

It must be a straight prism, otherwise it can't be solved. If it's a diagonal prism, it lacks the condition of angle
Side edge length x, as long as X satisfies 4 - √ (x ^ 2-100) > 0; 100

In the plane rectangular coordinate system, if point a (x, y) is given the same sign as XY, then which quadrant point a may be in
(2) If XY is different, which quadrant is point a possible in (3) if xy = 0, what are the possible positions of point a

(1) If XY has the same sign, point a may be in quadrant 1 and 3
(2) If XY is different, point a may be in quadrant 2 and 4
(3) If xy = 0, the position of point a may be in the positive half axis of X axis, the negative half axis of X axis, the positive half axis of Y axis, the negative half axis of Y axis and the origin

The road construction site has transported 2000 cubic meters of concrete. The width of the road is 8 meters and the thickness is 25 cm. How much concrete can be paved

If it can be laid x meters long, there will be
8*0.25*X=2000
It is concluded that x = 1000m

If 2A + B = 1, a > 0, b > 0, then the minimum value of a ^ 2 + B ^ 2 is obtained

a^2+b^2≥2ab
If and only if a = B, the equal sign holds
Here a = b = 1 / 3
So the minimum value is 2 × (1 / 3) × (1 / 3) = 2 / 9

Characteristics of silk

Silk, also known as "natural silk", is a continuous long fiber formed by the solidification of silk liquid secreted by mature silkworms when they cocoon. Like wool, it is one of the earliest animal fibers used by human beings. According to different foods, it can be divided into silkworm, tussah, cassava, camphor, willow and sky silkworm, etc, It is made of two single fibers bonded and wrapped with sericin. Several cocoon filaments are pulled out and wrapped with sericin. The filaments are divided into mulberry silk (also known as raw silk) and tussah silk, which are collectively referred to as silk. The silk without sericin is called refined silk. With them as raw materials, it can be processed into various kinds of fabrics by loom
Silk fiber is composed of two triangular or semi elliptical silk fibroin wrapped with sericin, and its cross section is elliptical. Silk fiber is protein fiber, and sericin and sericin are its main components, among which sericin accounts for about 3 / 4 and sericin accounts for about 1 / 4. Sericin and sericin are composed of 18 kinds of amino acids, containing about 97% pure protein. Sericin is a spherical protein with good water solubility, The degumming and scouring of silk in hot water takes advantage of this property of sericin. Due to the different amino acid composition of sericin and silk fibroin, silk fibroin is fibrin and silk fibroin is globulin. The total length of silk from silkworm can reach more than 1000 meters
I. characteristics of mulberry silk
Physical properties of mulberry silk
Silk is a porous protein fiber with good moisture absorption, moisture dispersion, air content and air permeability. The limbs are soft and comfortable, with unique "silking" characteristics
2. The breaking strength and elongation of silk are 3.3.6dn/tex (3.50 ~ 4.09gf / denier), 15 ~ 25% and 432.471.4n/mm ~ 2 (44 ~ 48kgf / mm ~ 2), which are close to steel wire. The wear resistance of silk is better than other natural fibers, and 22.2 / 24.42dtex (20 / 22 denier) 4A count raw silk bales and strength are about 80 times
3. Silk has good heat resistance, and its decomposition point is about 150 ℃. At the same time, silk has good heat preservation, and it feels warm in winter and cool in summer
4. Silk has good insulation property and is a bad conductor of electricity. However, when the moisture regain is high, the resistance will be reduced and the insulation property will be reduced. Generally, the moisture regain of silk fiber is 8% ~ 14%
5. Silk has good dyeing performance. It can be dyed with direct dyes, acid dyes, reactive dyes and a variety of mordants. Basic dyes need protective agents. The dyeing effect is beautiful, bright and delicate
6. The resistance of silk to acid is stronger than cotton and weaker than wool. With the increase of concentration and temperature, silk fiber stops swelling and dissolves. Caustic alkali can dissolve sericin and damage silk fibroin even at low temperature
7. The silk fibroin in silk can absorb some metals (such as tin). With this property, tin incremental processing can be carried out to increase the volume and wrinkle resistance of silk fibroin. Sericin fixation can also be used to treat silk to obtain new silk materials with unique style and to make some clothing accessories and summer clothing
8. The defect of silk fiber is that it is easy to cause yellowing and embrittlement after long-term storage or exposure to the sun. The silk fabric is also easy to fade after washing and then exposed to the sun. Some microbial fungi can make the silk color change and affect the quality of silk fabric. In addition, the wearing properties of the fiber, such as friction strength, buckling strength and stretching fatigue, are not as good as those of synthetic fiber
Characteristics of mulberry silk
1. Comfort. Silk is made up of protein fiber, which has excellent biocompatibility with human body. In addition to its smooth surface, its friction stimulation coefficient to human body is the lowest among all kinds of fiber, only 7.4%. Therefore, when our delicate skin meets the smooth and delicate silk, it follows the curve of human body with its unique soft texture, Take good care of every inch of our skin
2. Good moisture absorption and desorption. Silk protein fiber is rich in many hydrophilic groups such as amino (- chnh) and amino (- NH2). Because of its porous nature, it is easy for water molecules to diffuse, so it can absorb or emit water in the air, and maintain a certain amount of water. Under normal air temperature, it can help the skin to retain a certain amount of water without making the skin too dry, Because of this property, silk fabrics are more suitable for direct contact with human skin. Therefore, people regard silk clothing as one of the necessary summer clothes
Silk not only has good heat dissipation performance, but also has good heat preservation performance. Its heat preservation performance is proud of its porous fiber structure. There are many very small fibers in a silk fiber, and these small fibers are composed of smaller fibers. Therefore, more than 38% of the seemingly solid silk is hollow, and there is a lot of air in these gaps, The air prevents the heat from escaping, making the silk very warm
3. Sound absorption, dust absorption and heat resistance. Silk fabric has high porosity, so it has good sound absorption and air absorption. Besides making clothes, it can also be used for interior decoration, such as silk carpet, tapestry, curtain, wall cloth, etc, Because silk has the properties of moisture absorption, moisture release, moisture retention, air absorption and porosity, it can also adjust the indoor temperature and humidity, and absorb harmful gases, dust and microorganisms. In addition, the thermal denaturation of silk fiber is small, and it is relatively heat-resistant. When it is heated to 100 ℃, only about 5 ~ 8% of it is brittle, The thermal variability of most synthetic fibers is 4 ~ 5 times larger than that of silk. The combustion temperature of silk is 300 ~ 400 ℃, which is flame-retardant, while the combustion temperature of synthetic fiber is 200 ~ 2600C, which is flammable and fusible. Therefore, using silk fiber as the raw material of interior decoration can not only play the role of sound absorption, dust absorption, heat preservation, but also play the role of flame retardant
4. Anti ultraviolet. Tryptophan and tyrosine in silk protein can absorb ultraviolet rays, so silk has better anti ultraviolet function. Ultraviolet rays are very harmful to human skin. Of course, after absorbing ultraviolet rays, silk will undergo chemical changes, which makes silk easy to turn yellow under sunlight
From the Internet

For a certain mass of carbon dioxide, when its volume v = 5m to the third power, its density p = 2kg / m3 (1), find the functional relationship between P and V
When v = the third power of 9m, the density p of carbon dioxide can be calculated

∵ density formula: ρ = m / V
∴m=ρV=10kg
That is, the functional relationship between ρ and V is: ρ = 10 / v
ρ=10/V=10/9 kg/m³

On the roots of the quadratic equation (x + m) ^ 2 = n ^ 2 of X