N = (X-Y) / (x + y)... Finding the partial derivatives of X and Y respectively It's an / ax, an / ay There is a problem of calculating uncertainty transfer formula in physics experiment, but I haven't learned how to solve this problem

N = (X-Y) / (x + y)... Finding the partial derivatives of X and Y respectively It's an / ax, an / ay There is a problem of calculating uncertainty transfer formula in physics experiment, but I haven't learned how to solve this problem

N = (X-Y) / (x + y) to calculate the partial derivative of X and Y respectively. In fact, to calculate the partial derivative is the same as to calculate the derivative, except that we used to study the derivation of one variable, but now it is the derivation of two variables. If you want to calculate the partial derivative of X, then you can take y as a constant, and there are: an / ax (where a is the negative sign of the partial derivative) = [1 * (x + y) - (X-Y)] / (x + y) ^ 2 = 2Y / (x

Well, my question is not to forget to write DX. The correct answer is dy = [(y-xy) / (xy-x)] DX, which can be obtained by taking logarithm left and right. But why is it different from the above answer? This is my question

Notice that e ^ {x + y} = XY is brought into your expression to simplify dy = (y-xy) / (xy-x) DX

How to deal with a DC ammeter with a range of 1mA and an internal resistance of 1 ohm if it is to be expanded to 100mA

Connect a resistor in parallel
The resistance R is:
U=ir=1.*1=1mV
I = I quantity - I = 100-1 = 99ma
R = u / I = 1 / 99 = 0.01 ohm = 10 milliohm. It's easy to buy

1. A workshop has contracted 50 sets of assembly machines, which are required to be completed on time and in quantity. Due to the technical innovation, two more machines can be assembled every day. As a result, the workshop not only completed the task 2 days earlier than the contract, but also assembled 6 more machines. How many days is the time stipulated in the contract? How many machines can be assembled every day?
2. In 1998, during the flood fighting and disaster relief in Hubie, a certain company was ordered to send a platoon to Gongan County, 90 kilometers away from the station, for emergency rescue. One hour and 45 minutes later, due to the dangerous situation at home, company B was sent to support by car. It was known that company B was 28 kilometers faster than platoon a per hour, just catching up with platoon a third of the whole journey
(1) Find the time it takes company B to catch up with platoon a
(2) When company B catches up with platoon a, the superior orders platoon a to go to a city 24 kilometers away to carry out the task, and requires platoon A and company B to arrive at their designated locations at the same time. How many kilometers should platoon a speed up per hour?

Let the assembly time be x days, 56 / (X-2) = 50 / x + 2x = 10 or - 5, so x = 10. Note to test 2. Let the first platoon travel x kilometers per hour (30 kilometers in one third) 30 / X-7 / 4 = 30 / (x + 28) and get X1 = 12, x = - 40 (rounding off) the speed of the second platoon is 40 km / h, and the speed of the second platoon to reach the designated place is 60 / 4

About the physical power transmission of senior two,
This section says that the output power to the user is certain, increase the output voltage of the generator, reduce the power loss (in the principle of transformer, the input voltage of the primary coil determines the output voltage of the secondary coil, and the output voltage determines the output power, so the input voltage of the primary coil changes, and the output power of the secondary coil changes accordingly.), So why does the output voltage of the generator increase (the input voltage of the primary coil increases) and the power of the consumer (the output power of the secondary coil) remain unchanged in the chapter of electric energy transmission? Isn't this contradictory?

The input power of transformer is determined by the output power
Increasing the output voltage means that when the maximum input power is constant, increasing the input voltage can reduce the current and reduce the power loss on the wire
There is no contradiction
Ask again if you don't know

The composition is about 600 words

In everyone's heart, there is a treasure of your own. It may be a gift from your friends and classmates; it may be a reward from your parents; it may be a story worth remembering in your deep memory But what about me? I'm different from them One afternoon, all of a sudden, dark clouds were all over the place

What is the relationship between the work done by Ampere force and Joule heat? How to understand? Please explain in detail!

The essence of electromagnetic induction phenomenon is the process of different forms of energy conversion. The process of generating and maintaining the existence of induced current is the process of other forms of energy conversion into induced current electric energy. 2. The process of Ampere force doing positive work is electric energy

First simplify and then evaluate (a-b / A + b) (a ^ 4-A ^ 2B ^ 2 / A ^ 2-AB), where a = 2, B = 3

［（a－b）/（a＋b）］［（a^4－a^2b^2）/（a^2－ab）］
＝［（a－b）/（a＋b）］［a（a^2－b^2）/（a－b）］
＝［1/（a＋b）］a（a－b）（a＋b）
＝a（a－b）
＝2×（2－3）
＝－2
Note: please pay attention to the correct use of brackets to avoid misunderstanding

The power supply voltage of the electric vehicle is 36V, the coil resistance of the motor is 1 ohm, the current passing through the motor is 5A when working, and what is the electric power consumed by the motor when working
Please write the calculation process

180w

After braking, a car moves in a straight line with uniform deceleration. When timing starts from braking, the speed at the end of 2S is 6m / s, and the displacement of the car is 4m in one second from 2.5s to 3.5s

1. "From 2.5 s to 3.5 s, the displacement of the car is 4 m" means that the speed at the end of the third second is 4 m / s
Acceleration a = (v2-v1) / T = (4-6) / (3-2) = - 2m / S ^ 2
Initial velocity V0 = V1 at = 6 + 2 * 2 = 10m / S
Because the deceleration time t0 = V0 / a = 10 / 2 = 5S, the displacement within 6S after braking is s = (V / 2) * t0 = 25m