In school, I see children's smiling faces and the sound of reading every day

In school, I see children's smiling faces and the sound of reading every day

In school, I see children's smiling faces every day and hear their reading sounds

In school, I see children's smiling faces and reading sounds every day

In school, I see the children's smiling faces every day and hear the sound of reading

Calculation of 199.199x198-198.198x199 by simple method

199.199x198-198.198x199
=(199*198+0.199*198)-(198*199+0.198*199)
=0.199*198-0.198*199
=0

The problem of deriving derivative function from implicit function
I'm a little confused about the derivation of a function from an implicit function. For example, in an application problem, the increment of a balloon's surface area is 100 to calculate the radius increment. The area formula is s = 4 * Pai * R2. My first impression is that s' = 8 * Pai * R after seeing the teacher, what's the difference between the upper and lower formulas of s' = 8 * Pai * r * r ', These two formulas are very confusing
If the radius of a circle is increased from 1 to 1.002, and the change of the area of a circle is calculated in differential form, then do you want to use the above formula or the following formula

It can be said to be the same: s' = 8pai * r, that is, DS / DR = 8pai * r
S' = 8 * Pai * r * r 'denotes DS / DR = 8pai * r * DR / DR (derivation of R)

We know that a + B + C = 1, and prove that ab + BC + Ca is less than or equal to one third

The simplest explanation of special relativity

Special relativity mainly describes the relationship between the motion of matter in inertial frame and other reference frames. For example, when a spaceship flies near the speed of light relative to your reference frame, you will observe that the time in the spaceship will slow down, the distance will shorten and the mass will increase

3x-4（2x+5)＝7（x－5）＋4（2x＋1）
Need process

The original formula is: 3x-8x-20 = 7x-35 + 8x + 4
3x-8x-7x-8x=-35+4+20
-20x=-11
x=11/20

After a rectangle is divided into two squares of equal size, the perimeter increases by 12 decimeters. What is the original area of the rectangle? What is the original perimeter?

After the rectangle is divided into two equal squares, the sides of the two squares are added, that is, the width and length of the rectangle are 12 decimeters
Formula: Area: 12x (12 △ 2) = 72 square decimeters perimeter: (12 + 6) x2 = 36 decimeters
A: the original rectangular area is 72 square decimeters, the original perimeter is 36 decimeters
100% right! Believe me!

The rotational speed is 7.5rad/min, what is the angular speed rad / S

If you look at the unit, one is per minute and the other is per second, so 7.5/60 =? Rad / s

Solving equation 3 / x + 1 / (x-4) = (3x + 16) / (x + 4) - 3

3/x+1/(x-4)= (3x+16)/(x+4)-3
[3(x-4)+x]/x(x-4)=(3x-12+28)/(x-4)-3
4(x-1)/x(x-4)=3+ 28/(x-4) -3
4(x-1)=28/(x-4) * x(x-4)
4(x-1)=28x
x-1=7x
6x=-1
x=-1/6