It is proved by analysis that if a, B ∈ R and a ≠ B are known, then | 1 / (A & # 178; + 1) - 1 (B & # 178; + 1) | a-b|

It is proved by analysis that if a, B ∈ R and a ≠ B are known, then | 1 / (A & # 178; + 1) - 1 (B & # 178; + 1) | a-b|

On the left
That is to say, | (B-A) (B + a) / (A & # 178; + 1) (B & # 178; + 1) | = 0
So when a > 0, b > 0
a+b

The rated voltage is 220 V, the resistance is 24.2 ohm of an electric water heater, in the normal work, how much is its electric power? Work 0.5 hours generated by the heat is more
When an electric water heater with rated voltage of 220 V and resistance of 24.2 Ω works normally, how much is its electric power? What is the heat generated when it works for 0.5 h?

P=U^2/R=220×220÷24.2＝2×10^3 w=pt=2×10^3×0.5=1×10^3

The height of a street lamp is h from the ground, and the height of a person is L
Find 1 to prove that the shadow on the top of the head moves in a straight line at a constant speed
2 find the change rate of the length of the shadow with time

Answer: according to similar triangle method and other methods
Suppose: the street lamp is at O, and people move to the right along the horizontal ground,
1. When people are directly under the street lamp,
The head is at a,
People's feet are at C, so is the shadow on the top of the head;
2. When the person is not directly under the street lamp,
The top of the head is at B, and the shadow of the top of the head is at D
Then, △ OAB and △ OCD are similar
CD/AB=h/(h-L)（1）
Because people are moving in a straight line at a constant speed,
Of course, the head is moving in a straight line at a constant speed. Then AB = V * t (2)
(2) By substituting (1), CD = H / (H-L) * V * t
That is: the shadow D on the top of the head is moving in a straight line at a constant speed,
The velocity is: H / (H-L) * v

Is kinetic energy the basic unit of the international system of units

Kinetic energy unit is not the basic unit in the international system of units
The seven basic physical quantities in the international system of units are:
Length m
Mass kg
Time s
Current a
Thermodynamic temperature K
Luminous intensity CD
Amount of substance

As shown in Figure 3-12, there are two pieces of wood 1 and 2 with mass M1 and M2 on a rough horizontal plane
As shown in the figure, on a rough horizontal plane, there are two wooden blocks 1 and 2 with mass M1 and M2 respectively. In the middle, they are connected by a light spring with original length of L and stiffness coefficient of K. The dynamic friction coefficient between the wooden block and the ground is μ. Now, a horizontal force is used to pull the wooden block 2 to the right. When the two wooden blocks move at a uniform speed together, The distance between the two pieces of wood is () (2001 national college entrance examination of Science) [5] (a) l + (μ / k) m1g (b) l + (μ / k) (M1 + m2) g (c) l + (μ / k) m2g (d) L + (μ / k) [(m1m2) / (M1 + m2)] G

In this question, just look at 1. The wood block 1 has a uniform speed, so the force must be balanced. Its friction force is um1g, so the spring tension must be um1g. Therefore, according to this, we can calculate the length of the spring extension, and the original length is the answer

How many square decimeters is one square meter equal to

100

A metal block with a volume of 0.1 cubic decimeter. If the metal block is immersed in water and the spring scale shows 6.8 n, calculate the buoyancy, gravity and density of the object

Because it's submerged in water
So V object = V row
So f floating = ρ water V discharging g = 1.0 × 10 ^ 3 × 0.1 × 10 ^ (- 3) × 10 = 1n
So g weight = 1 + 6.8 = 7.8n
Because g = mg
So m = g / g = 7.8 / 10 = 0.78kg = 780g
The results show that ρ = m / v = 780g / 100cm ^ 3 = 7.8g/cm ^ 3

If the length of the two right angles of a right triangle is a, B, the length of the hypotenuse is C, the height h on the hypotenuse, 1 / 2 of a + 1 / 2 of B = 1 / 2 of H

The area of triangle = (1 / 2) AB = (1 / 2) ch, we can get: ab = ch;
From Pythagorean theorem we can get: A & # 178; + B & # 178; = C & # 178;
So, 1 / (A & # 178;) + 1 / (B & # 178;) = (A & # 178; + B & # 178;) / (AB) & # 178; = C & # 178; / (CH) & # 178; = 1 / (H & # 178;)

The mass of two cuboid blocks is M1 and M2 respectively, which are stacked on the inclined plane with an inclination angle of θ
It is known that the dynamic friction coefficients between M1 and M2, M2 and inclined plane are μ 1 and μ 2, respectively. They keep relatively static from static, and accelerate down along the inclined plane together, and the friction between M1 and M2 decreases
A. It could be zero
B. It is equal to μ 2m1gcos θ
C. It is equal to μ 1m1gcos θ
D. The direction of friction on M1 is upward along the inclined plane

Choose C
The first step: take M1 and M2 as a whole, do force analysis, and get an equation
（m1+m2）gsinθ-μ2（m1+m2）gcosθ=（m1+m2）a
A = GSIN θ - μ 2gcos θ is obtained
Step 2: take M1 out separately, do force analysis, and get an equation
m1gsinθ-f=m1a
Then f = m1gsin θ - m1a
=μ2m1gcosθ
Choose C

Last year's profit was negative and this year's profit is positive. How to calculate the profit growth rate?
Scheme 1: for example, if it was - 100000 last year and 100000 this year, the growth rate is = | (10 - (- 10)) / (- 10) | = 200%. Scheme 2: if it was - 1000000 last year and 100000 this year, the growth rate is = | (10 - (- 100)) / (- 100) | = 110%. Obviously, the growth rate of scheme 2 is higher than that of scheme 1. It is wrong to take absolute logarithm. Please help those who are good at statistics

That's right. Isn't it too sharp? In my opinion, it's just the growth rate based on different base numbers. The two can't be compared