Z = f (XY, y) for DZ Finding the total differential of Z

Let u = XY
v=y
z=f(u,v)
dz=f1`du+f2`dv
du=xdy+ydx
dv=dy
Substituting, yes
dz=f1`(xdy+ydx)+f2`dy
=y*f1`dx+(x*f1`+f2`)dy
Where F1 'and F2' denote the partial derivatives of the first and second parameters of F respectively

Let a and B be nonzero real numbers, then y = A / | a | + | B | / B + C / | C |, which belongs to the set classification
What kind and why?

The condition should be that a, B and C are all non-zero real numbers, right?
If all three are positive numbers, then y = 3,
If there is a negative number and two positive numbers, then y = 1,
If there are two negative numbers and one positive number, then y = - 1,
If all three are negative, then y = - 3,
Therefore, the value set of Y is {- 3, - 1,1,3}
This is a finite set

A school party prepared three kinds of drinks, average 2 people drink a bottle of a drink, 3 people drink a bottle of B drink, 4 people drink a bottle of C drink, a total of 65 bottles, ask how many people attend the party?

X/2+X/3+X/4=65
6X/12+4X/12+3X/12=65
13X/12=65
13X=65*12
X=60

Simplify (A's Square - B's Square) divided by (a + b) + (A's Square - 2Ab + B's Square) divided by (a-b)

(a^2-b^2)÷(a+b)+(a^2-2ab+b^2)÷(a-b)
=(a-b)(a+b)÷(a+b)+(a-b)^2÷(a-b)
=(a-b)+(a-b)
=2a-2b

The distance between a and B is 40 km, the speed of motorcycle is 45 km / h, and the speed of truck is 35 km / h. how long does it take for the two vehicles to travel at the same time
10 km apart? (solving equation)

Obviously, there are two situations to consider. First, before the meeting, the two vehicles will travel a total of 30 kilometers: set the time as X
45x+35x=40-10
80x=30
x=3/8
The second is after meeting: set the same time as X, then there are: (don't forget this situation!)
45x+35x=40+10
80x=50
x=5/8
If you don't know anything, you can ask me at any time!

Given the equation system a + 2b-17c = 0, 3b-2a-15c = 0, the ratio of C is equal to 0 in the period, the value of A-B + C / A + B-C is obtained

The original method: A and B are represented by C, and then substituted by A-B + C / A + b-c

Both a and B vehicles leave from a and B at the same time. It is known that a vehicle travels 50 kilometers per hour and B vehicle 40 kilometers per hour

Liu Guanchao, there are two kinds: 1, a and B two cars from a, B two places at the same time, a car 50 kilometers per hour, B car 40 kilometers per hour, when a car passed a, B distance of 1 / 3 more than 50 kilometers, meet B car. A, B two places together how many meters? Set the distance between the two places x kilometers (x / 3 + 50) / 50 = (x-x / 3-50) / 404

If the solution of equation 6x + 7-2m = 2x + 3 is greater than 2 and less than 10, the value range of M is obtained

4x=2m-4
x=2m-4/4=m-2/2
two

The speed of a car is 47 times that of a train. Two cars are running from two places at the same time, and they meet at a distance of 15 kilometers from the midpoint. How many kilometers does the train travel?

The distance of the whole journey: 15 △ 74 + 7-12, = 15 △ 322, = 110 (km), the distance of the train: 110 × 711 = 70 (km). A: at this time, the train runs 70 km

If the denominator is not 101001000,..., you need to use () to remove () numerator. If you can't divide it completely, you can press () to keep several decimal places

If the denominator is not 101001000,..., it is necessary to use (denominator) to remove (divide) the numerator. If the division is not complete, you can keep several decimal places according to (rounding method)

Z = f (XY, y) for DZ Finding the total differential of Z