Vector formula is often used to explain electromagnetic field In this formula, there are both gradients to a and divergence to A. why? I think only scalar can find gradients and only vector can find divergence. So why can a be found?

Vector formula is often used to explain electromagnetic field In this formula, there are both gradients to a and divergence to A. why? I think only scalar can find gradients and only vector can find divergence. So why can a be found?

This formula actually defines how to calculate when Laplace operator acts on a vector, which is the formula on the far right. You think that only scalar can calculate gradient and only vector can calculate divergence, which is correct. But don't forget that gradient is a vector and divergence is a scalar. For example, the formula on the right of equal sign

What are the main advantages of online market research compared with traditional market research methods

Advantages
1. Fast
2. Low cost
3. Wide coverage
4. Convenient data statistics
shortcoming
1. No valid samples can be collected
2. High error rate of information collection
I'm glad to answer for you,

What kinds of traditional cultural features does the tomb of three kings reflect? What are the artistic features?

The tomb of three kings can be regarded as the product of Taoist school in the spring and Autumn period and Warring States period. The article is related to the "humanitarian ethics" of Taoism. In the "humanitarian ethics", there are monarchs and ministers (the relationship between the leader and the LED), monarchs, courtiers and ministers. In the workplace, superiors bully subordinates and subordinates rebel against superiors or units

Several mathematical problems, but please be sure to write the process and the formula or theorem used,
1, Let f (x) = x & # 178; - 1, then f (x + 2) =?
2, sin (180 ° + α) = 1 / 3, then cos (270 ° + α) =?
3, what is the minimum positive period of y = sin2 / 1X?
4, function f (x) = x & # 179; + ax & # 178; + 3x-9, if f (x) is known to have an extreme value when x = 3, then a =?
5, the minimum positive period of the function y = 2sinxcosx + 1-2sin & # 178; X is?
Since we have completely forgotten mathematics, we should try to find out the answers and formulas or theorems in detail. We have no points, so we can only offer a reward of 10 points,

1、F(x+2)=(x+2)²-1=x²+4+4x-1=x²+4x+3
2、cos(270°+α)=cos(270°+α-360°)=cos(α-90°)=cos(90°-α)=sinα=-sin(180°+α)=-1/3
3. It's y = sin1 / 2x. If it is, it's 720 degrees. No, it's 180 degrees
4. The derivative of F (x) = 3x & # 178; + 2aX + 3 is zero when x = 3, so a = - 5
5. Y = 2sinxcosx + 1-2sin & # 178; X = sin2x + cos2x = (radical 2) sin (2x + 45 °)
So the minimum positive period is 180 degrees

david bought 100 rubbers for $200 .he sold 30% of them at a price of $4 each and then sold the remaining rubber at $3 each .find the percentage change.

the total money he get from solding all rubbers=30*4+70*3=$330
so the changed percentage=330/200=165%

Frequency and frequency
The following mistakes are
1. The higher the frequency, the higher the frequency
2. The sum of all frequencies is equal to 1
3. Frequency represents the number of occurrences of each object
4. Frequency must be a positive number
And explain the cause of the error

1 wrong
Frequency refers to the proportion of frequency in the total number,
Suppose the frequency of a is 2, the total number is 10, and the frequency is 0.2
The frequency is 3, the total number is 30, and the frequency is 0.1
The frequency is large, but the frequency is small
4 error can be 0

One third: one half simplification
Simplification ratio

1/3:1/2
=1/3×6:1/2×6
=2:3

Conversion of mathematical expression to high level language expression
How to express 5 △ 2 × (3 + 6) + (7-3)] into high-level language?

5/(2*(3+6)+(7-3))

There are four numbers 3, - 5, - 13, 7, through which formula the result is equal to 24

[（-5)×（-13)+7]/3=24

Factorization of mathematics in grade three
1.（2x-3）²-2x+3=0
It requires a process

(2x-3)²-2x+3=0
(2x-3)²-(2x-3)=0
(2x-3)(2x-3-1)=0
(2x-3)(2x-4)=0
x1=3/2 x2=2