There is a uniform magnetic field in the vertical direction between two parallel metal plates with length L and spacing L. as shown in the figure, the magnetic induction intensity is B, and the positive ions with mass m and charge q are injected into the magnetic field from the midpoint of the left end of the parallel plate in the direction parallel to the metal plate; ①v＜qBL4m②v＞5qBL4m③v＞qBLm④qBL4m＜v＜5qBL4m. A. ①②B. ①③C. ②③D. ②④

There is a uniform magnetic field in the vertical direction between two parallel metal plates with length L and spacing L. as shown in the figure, the magnetic induction intensity is B, and the positive ions with mass m and charge q are injected into the magnetic field from the midpoint of the left end of the parallel plate in the direction parallel to the metal plate; ①v＜qBL4m②v＞5qBL4m③v＞qBLm④qBL4m＜v＜5qBL4m. A. ①②B. ①③C. ②③D. ②④

According to QVB = mv2r, r = mvqb. If the particle just shoots from the left side, as shown in the figure, then R1 = L4. So V1 = qbl4m. If the particle just shoots from the right side, as shown in the figure, R22 = L2 + (R2 − L2) 2, then R2 = 5l4. So V2 = 5qbl4m. If the ion does not hit the plate, then V ＜ V1 or V ＞ v2. So a is correct, B, C and D are wrong. So a

Can the result be regarded as the derivative of the function and then multiplied by DX?
For example, y = sin (4x + 2), Y & # 180; = 4cos (4x + 2); dy = 4cos (4x + 2) DX
Can you look at it like this

Yes, that's it. Y 'is actually dy / DX. For the previous answer, I think there is a problem. It's not that the formula after derivation is added with a constant, but that the formula after integration is added with a constant

Solving differential equation: 2x (ye Λ X & #178; + 2x & #178;) DX = e Λ X & #178; dy
The mathematical signs in the formula are only +, = and Λ (power sign), and the rest are numbers and unknowns

2x(ye^x^2+2x^2)dx=e^x^2dy
ye^x^2dx^2-e^x^2dy=-4x^3dx
yde^x^2/e^x^4-dy/e^x^2=de^(-x^4)
d(y/e^x^2)=de^(-x^4)
y/e^x^2=e^(-x^4)+C
General solution y = e ^ (- x ^ 2) + CE ^ x ^ 2

Given that the points a (x1, Y1), B (x, Y2), O are the coordinate origin, the vector OA × ob satisfies: absolute value OA + ob = absolute value oa-ob
Let the equation of circle C be x2 + Y2 - (x1 + x2) x - (Y1 + Y2) = 0

From | OA + ob | = | oa-ob|
The two sides are squared, the terms are shifted, and the similar terms are merged
OA·OB=0
OA ⊥ ob
From the conclusion of the textbook:
x1*x2+y1*y2=0
You can prove it yourself
In this way, the left side of the equation that brings the coordinates of a into the circle is as follows:
x1²+y1²-(x1+x2)*x1-(y1+y2)*y1
=x1²+y1²-x1²-x1*x2-y1²-y1*y2
=-(x1*x2+y1*y2)
=0 = right
So we know that a is on the circle,
Similarly, B is on the circle
That is to say, AB is the string of a circle,
It is also known that the center of circle C is ((x1 + x2) / 2, (Y1 + Y2) / 2)
It's exactly in AB, that is, AB passes through the center of the circle
So AB is the diameter of circle C

1. If there are 18 tons left, how many tons are there in this pile of yellow sand
2. If 22 tons of yellow sand are used twice, how many tons of yellow sand are there? 3. If 2 tons more are used in the first time than in the second time, how many tons of yellow sand are there in total

There are 36 tons of yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand is 44 tons in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the yellow sand in the Yellow there are 12 tons of sand

The graph () of the function y = sin (x + π 3)
A. On the origin symmetry B. on the line x = π 6 symmetry C. on the y-axis symmetry D. on the line x = − π 3 symmetry

In the function y = sin (x + 13 π), let x + 13 π = k π + 12 π, K ∈ Z, we can get x = k π + π 6, K ∈ Z, so the symmetry axis is, we can get x = k π + π 6 & nbsp; so B is correct. Let x + 13 π = k π, K ∈ Z, we can get the abscissa of the symmetry center x = k π - 13 π, so the symmetry center is (K π - 13 π, 0), K ∈ Z, so B is selected

The number of female workers in a textile factory is 100 more than 75% of the total number of workers in the factory. The number of male workers is 20% of that of female workers. How many female workers are there in this textile factory?

There are x female workers and 20% x male workers
(X+20%X)×75%+100=X
120%X×75%+100=X
90%X+100=X
X=1000
There are 1000 female workers

If the quadratic trinomial 2x ^ 2 + kx-15 (k is an integer) can be factorized in the range of integers, please write the possible value of K

2X ^ 2 + kx-15 (k is an integer) can be factorized in the range of integers
Then: △ = K & # 178; + 120 is the complete square form
When K & # 178; = 1, △ = 121 = 11 & # 178;
When K & # 178; = 49; △ = 169 = 13 & # 178;
So, k = 1 or - 1; k = 7 or - 7

Girls make up one third of the total in the school chorus, and then three more came to join
At this time, the number of girls stands at 3 / 8 of the total number of the chorus?
The process of solving the equation should be more detailed. I have no choice but to solve the equation. I don't quite understand. Why do I feel that 72 or 48 is right?

Suppose there are x people in the chorus, then there are x-3 people in the original chorus
1 / 3 × (x-3) + 3 = 3 / 8
1 / 3 X-1 + 3 = 3 / 8 x
1 / 3 x + 2 = 3 / 8 x
3x of 8 - 1 of 3 = 2
(3 / 8-1 / 3) x = 2
1 in 24 = 2
X = 2 / 24
x＝48

(x2-3x) 2 - (3x-1) 2 factorization

（X2-3X）2-(3X-1)2
=(x^2-3x)^2-(3x-1)^2
=(x^2-3x-3x+1)(x^2-3x+3x-1)
=(x^2-1)(x^2-6x+1)
=(x-1)(x+1)(x^2-6x+1)