1.(a-2+b)(a+2+b)2.(x^5y^3-2x^y^2+3/4x^2y^2)/1/12x^2y^2

1.(a-2+b)(a+2+b)2.(x^5y^3-2x^y^2+3/4x^2y^2)/1/12x^2y^2

(a-2+b)(a+2+b)
=(a+b)^2-2^2
=a^2+b^2+2ab-4
(x^5y^3-2x^y^2+3/4x^2y^2)/1/12x^2y^2
=(x^5y^3-5x^2y^2/4)*12/x^2y^2
=x^2y^2(x^3y-5/4)*12/x^2y^2
=12x^3y-15

Given that a = 3x to the second power - 2mx + 3x + 1, B = 2x to the second power - MX + 3, and the value of 2a-3b has nothing to do with X, find the value of M

2A=6x^2-4mx+6x+2
3B=6x^2-3mx+9
2A-3B
=-mx+6x-7
=(6-m)x-7
6-m=0
m=6

If the polynomial of X, Y: x ^ (m-2) y ^ 2 + MX ^ (m-2) y + NX ^ 3Y ^ (M-3) - 2x ^ (M-3) y + m + n is reduced to a quartic trinomial, the value of M, n can be obtained
It requires a process, not a direct answer. The more detailed the better,

Quartic trinomial
So up to four times
X ^ (m-2) y ^ 2 times = m-2 + 2 = m
MX ^ (m-2) y times = m-2 + 1 = M-1
Nx ^ 3Y ^ (M-3) times = 3 + M-3 = m
2X ^ (M-3) y times = M-3 + 1 = m-2
So the maximum is m
So m = 4
Then the original formula = x ^ 2Y ^ 2 + 4x ^ 2Y + NX ^ 3y-2xy + 4 + n
Obviously, it can't be a trinomial
So there is no solution

A new operation is defined: a * b = a + B - | ab | simplify 2 * (A-1) (where a
To process and analyze, be clear~

=2+(a-1)-|2(a-1)|
=1+a-|2a-2| (∵a

What is the tangent equation of the cube of x = 1 + T and y = t at t = 2?

x=1+t^2,y=t^3
The coordinates of the curve at t = 2 are (5,8)
Slope of tangent = (dy / DT) / (DX / DT) = 2T / (3T ^ 2) = 2 / 3T = 4 / 3
So the tangent equation is Y-8 = 4 / 3 * (X-5), that is 4x-3y + 4 = 0

It is known that two straight lines: L1: (3 + m) x + 4Y = 5-3m, L2: 2x + (5 + m) y = 8. When the value of M is, L1 and L2 intersect parallel and vertically
Please use the related knowledge of line and equation to solve

L1: (3 + m) x + 4Y = 5-3m L2: 2x + (5 + m) y = 8 L1: (3 + m) x + 4Y = 5-3m = = > y = [5-3m - (3 + m) x] / 4 L2: 2x + (5 + m) y = 8 = = > y = (8-2x) / (5 + m) 1. Intersection [5-3m - (3 + m) x] / 4 = (8-2x) / (5 + m) m ≠ - 1, - 7 2. Parallel K1 = K2, (3 + m) / 4 = - 2 / (5 + m) M = - 1, - 7 3

Rubik's cube formula E.M.S

Turn to the middle layer

3-0.6 of 4 = () 9 of 5-14 = () 1 and 7-0.875 of 8 = () 6 of 7 + (1 of 2-6 of 7) = ()
Simple operation
13 out of 7 - (6 out of 7 + 5 out of 14)
4 and 3 / 7 - (3 / 7 + 1 and 5 / 8) - 2 and 3 / 8

6 = (0.15) 5-14 9 = (61 / 14) 1-8 7-0.875 = (1) 7 / 6 + (2 / 1-7 / 6) = (1 / 2) simple operation 7 / 13 - (7 / 6 + 14 / 5) = 13 / 7-6 / 7-5 / 14 = 1-5 / 14 = 9 / 14; 4-7 / 3 - (7 / 3 + 1 / 8 / 5) - 2-8 / 3 = 4 + 3 / 7-3 / 7-1-5 / 8

The perimeter of a square is a meter. How many square meters is its area?

The perimeter of a square is a meter, and its area is A-16 square meters

Similarities and differences between DC motor and AC motor
Please don't just tell me that the power supply is different or the current direction changes one by one. I want to know the difference between the working principle of AC motor and DC motor
Why don't AC motors use commutators? Since the current of electromagnet and coil is changing, the force is equivalent to constant. Isn't it the same as DC motors? They also need commutators?

The function of motor is to convert electric energy into mechanical energy. Motor is divided into AC motor and DC motor
（1） AC motor and its control
AC motor is divided into asynchronous motor and synchronous motor. Asynchronous motor is divided into single asynchronous motor, two-phase asynchronous motor and three-phase asynchronous motor according to the stator phase number. Three phase asynchronous motor has the advantages of simple structure, reliable operation and low cost, which is widely used in industrial and agricultural production
1. Basic structure of three-phase asynchronous motor
The structure of three-phase asynchronous motor is also divided into two parts: stator and rotor
(1) Stator:
The stator is the fixed part of the motor, which is used to generate the rotating magnetic field
(2) Rotor:
Rotor is the key part. There are two kinds of rotor, squirrel cage type and wound type. Master their respective characteristics and differences. Squirrel cage type is used for small and medium power (below 100k) motors. Its structure is simple, reliable, and easy to use and maintain. Wound type can improve the starting performance and adjust the speed. The air gap between stator and rotor will affect the performance of the motor, Generally, the air gap thickness is 0.2-1.5mm
Master the connection method of stator winding
2. Working principle of three-phase asynchronous motor
Master the formula N1 = 60F / P, s = (N1-N) / N1, n = (1-s) 60F / P, and understand their significance (very important). You should be able to flexibly use these formulas for calculation. At the same time, remember: generally, the slip rate SN of motor under rated load is about 0.01-0.06
3. Data on the nameplate of three-phase asynchronous motor
(1) Model: master the examples in the book
(2) Rating: general understanding, master rated frequency and rated speed, China's frequency is 50 Hz
(3) Connection method: there are y type and angle type
(4) Insulation grade and temperature rise: master the definition of allowable temperature rise
(5) Working style: general understanding
4. Mechanical characteristics of three-phase asynchronous motor
Master the relationship between rated torque, maximum torque and starting torque. The formulas in the book should be mastered and flexibly used for calculation. At the same time, remember the following contents:
(1) When rotating at constant speed, the torque of the motor must be balanced with the resistance torque
(2) When the load torque increases, the initial instantaneous torque T (3) the overload coefficient of general three-phase asynchronous motor is 1.8-2.2
(4) When the motor is just started, n = 0, s = 1
5. Starting of three-phase asynchronous motor
(1) Direct start
When the motor starts at rated voltage, it is called direct start. The direct start current is about 5-7 times of the rated current. Generally speaking, the small capacity asynchronous motor with rated power less than 7.5kW can start directly
The electrical appliances used in the direct start control circuit include combination switch, button, AC contactor intermediate relay, thermal relay and fuse. Master their respective characteristics, and master the calculation of rated current of fuse
Direct start control circuit: master its control principle
(2) Reduced voltage starting of squirrel cage induction motor
Master the working principle of star angle starting and step-down starting of autotransformer
(3) Starting of wound three phase asynchronous motor
General understanding
6. Forward and reverse control of three-phase asynchronous motor
General understanding
7. Speed regulation of three phase asynchronous motor
It is important to understand the formula. There are three possibilities to change the speed of the motor, that is, to change the frequency, to change the number of poles of the winding or to change the slip
8. Synchronous motor
(1) Construction of synchronous motor
It should be compared with asynchronous motor
(2) Working principle of synchronous motor
It is known that the speed of synchronous motor is constant and does not change with the load
1. Working principle of DC motor
General understanding
2. Construction of DC motor
It is divided into two parts: the stator and the rotor. Remember that the stator and the rotor are composed of those parts. Note: do not confuse the commutator pole with the commutator. Remember the functions of the two
The stator includes: main magnetic pole, frame, commutating pole, brush device, etc
Rotor includes: armature core, armature winding, commutator, shaft and fan
3. Excitation mode of DC motor
The performance of DC motor is closely related to its excitation mode. Generally, there are four excitation modes of DC motor: DC separately excited motor, DC parallel excited motor, DC series excited motor and DC compound excited motor
DC separately excited motor: there is no electrical connection between the excitation winding and the armature, and the excitation circuit is supplied by another DC power supply. Therefore, the excitation current is not affected by the armature terminal voltage or armature current
DC shunt motor: the voltage at both ends of the shunt winding is the voltage at both ends of the armature, but the excitation winding is wound with thin wires, which has a large number of turns, so it has a large resistance, making the excitation current through it smaller
DC series motor: the excitation winding is connected in series with the armature, so the magnetic field in the motor changes significantly with the change of armature current. In order to avoid large loss and voltage drop in the excitation winding, the smaller the resistance of the excitation winding, the better. Therefore, DC series motor is usually wound with thicker wires, and its turns are less
DC compound motor: the magnetic flux of the motor is generated by the exciting current in two windings
4. Technical data of DC motor
Focus on the rated efficiency and rated temperature rise
Rated efficiency = output power / input power
Rated temperature rise refers to the maximum allowable value that the temperature of the motor is allowed to exceed the ambient temperature. The temperature rise on the nameplate refers to the maximum temperature rise of the motor winding
5. Mechanical characteristics of Shunt DC motor
Master the examples in the book
6. Starting, reversing and speed regulating of Shunt DC motor
(1) Start and reverse general understanding can be
(2) Speed regulation: there are three speed regulation methods for shunt motor
Change the flux
change voltage
Change the loop resistance of rotor winding
Master their respective advantages and disadvantages
2. Control motor
Control motor refers to the motor used for detection, comparison, amplification and execution in automatic control system
(1) DC servo motor
Master the classification and characteristics of permanent magnet DC servo motor; the difference between ordinary rotor permanent magnet DC servo motor and small inertia rotor DC servo motor
Working principle and performance of permanent magnet DC servo motor
Understand the working principle and grasp the performance
(2) AC servo motor
Generally understand the structure and working principle of AC servo motor, especially its performance
(3) Stepping motor
Master the advantages and main performance indicators of stepping motor, other general knowledge can be
The principle of AC motor: the electrified coil rotates in the magnetic field
Do you know the principle of DC motor? DC motor uses commutator to automatically change the current direction in the coil, so that the force direction of the coil is consistent and continuous rotation
Therefore, as long as the force direction of the coil is consistent, the motor will rotate continuously
AC motor is composed of stator and rotor. In your model, stator is electromagnet and rotor is coil. Stator and rotor use the same power supply, so the direction of current in stator and rotor always changes synchronously, that is, the direction of current in coil changes, and the direction of current in electromagnet also changes. According to the left-hand rule, the direction of magnetic force on coil remains unchanged, The coil can continue to turn
The function of the two copper rings: the two copper rings are equipped with the corresponding two brushes, and the current is continuously fed into the coil. The advantage of this design is that the winding problem of the two power wires is avoided, because the coil is constantly rotating. What would it be like if two wires were simply used to supply power to the coil?
As for the current in the coil, because it is alternating current, it is the moment when there is current equal to zero. However, compared with the time when there is current, this moment is too short. What's more, the coil has mass and inertia. Because of inertia, the coil will not stop
Reference: Baidu knows