Find the total differential of Z = XY / (X-Y), Why can't I do the same thing as the answer? Please help me with the detailed process,

Find the total differential of Z = XY / (X-Y), Why can't I do the same thing as the answer? Please help me with the detailed process,

Z = XY / (X-Y) DZ = f'x (x, y) DX + f'y (x, y) dyxy / (X-Y) takes partial derivative for X to get [y (X-Y) - XY] / (X-Y) & sup2; dxxy / (X-Y) takes partial derivative for y to get [x (X-Y) + XY] / (X-Y) & sup2; dy so DZ = [y (X-Y) - XY] / (X-Y) & sup2; DX + [x (X-Y) + XY] / (X-Y) & sup2; dy DZ = - Y & sup2; / (X-Y) & S

Z = sin (XY) + cos ^ 2 (XY) first order partial differential

Original function z = sin (x * y) + (COS (x * y)) ^ 2
əz/əx =y*cos(x*y) - 2*y*cos(x*y)*sin(x*y)
əz/əy =x*cos(x*y) - 2*x*cos(x*y)*sin(x*y)

The height of a cylinder is 6 cm. If the height is increased by 2 cm, the surface area of the cylinder will increase by 25.12 square cm. What is the volume of the original cylinder in cubic cm?

As the surface area increases, the bottom area does not change, so the side area increases
Therefore, the bottom perimeter * H = side area
Similarly, bottom perimeter * h increment = side area increment
So the perimeter of the bottom surface = 25.12 / 2 = 12.56 cm
Then the original side area of the cylinder is 12.56 * 6 = 75.36 square centimeter

It is known that a * 6 / 5 = 9 / 10 * b = 13 / 13 * C, and ABC is not equal to 0. Let's arrange the three numbers ABC in the order from large to small

Let their values be equal to 1, then a = 5 / 6, B = 10 / 9, C = 1, so B & gt; C & gt; a

Simple math problems in a high school
In the triangle ABC, if a ^ 2 * tanb = B ^ 2 * Tana is known, then what is the triangle
Please explain... I saw this problem in the preview (it should be very easy), "novice" please explain in detail
thank you

The solution ∵ TaNx = SiNx / cosx ∵ a ^ 2 * SINB / CoSb = B ^ 2sina / Cosa ∵ positive metaphysics Theorem A / Sina = B / SINB ∵ Sina ^ 2 * SINB / CoSb = SINB ^ 2 * Sina / Cosa ∵ simplified Sina * cosa = SINB * cob ∵ double angle formula sin2x = 2sinx * cosx ∵ sin2a = sin2b ∵ a = B or 2A + 2B = Πa + B = Π / 2, that is

Help arrange the time of homework (what time to write). It's better to finish it today, starting from 10 a.m
English: copy words, phrases, composition (about 75 minutes). One paper, one newspaper (80 minutes). Three newspapers (about 55 minutes). Morality: finish the exercise book (80 minutes)

At 10:00 in the morning, three Chinese newspapers will start for 55 minutes, with a 10 minute rest; at 11:05, English and composition will start for 75 minutes; at 2:00 to 5:00 in the afternoon, math will start at 5:00, 80 minutes to 6:30, with a 40 minute rest and dinner; at 7:10, morality will start for 80 minutes to 8:40. All homework will be finished

Given x + y = 6, xy = 8, find the value of 2x-xy + 2Y of X + 2XY + y

2X XY + 2Y of X + 2XY + y
=[2(x+y)-xy]/[(x+y)+2xy]
=(12-8)/(6+16)
=4/22
=2/11

[7 - (0.5 * 9.5 + 3 * 1 / 6)] * 8 / 21

[7 - (0.5 * 9.5 + 3 * 1 / 6)] * 8 / 21
=(7-4.75 + 0.5) * 8 / 21
=11 / 4 * 8 / 21
=22 out of 21

Finding all positive integer solutions of xy-x-y = 2
It's clear

xy-x-y+1=3
x(y-1)-(y-1)=3
(x-1)(y-1)=3
So X-1 = 1, Y-1 = 3 or X-1 = 3, Y-1 = 1 or X-1 = - 1, Y-1 = - 3 or X-1 = - 3, Y-1 = - 1
That is, x = 2, y = 4 or x = 4, y = 2 or x = 0, y = - 2 (rounding off) or x = - 2, y = 0 (rounding off)
The final result: x = 2, y = 4 or x = 4, y = 2

The school organizes tree planting activities. It is known that there are 27 trees planted in place a and 18 trees planted in place B. if the number of trees planted in place a is twice that of place B, how many people need to be transferred from place B to place a?

According to the meaning of the question, we get 27 + x = 2 (18-x), and the solution is x = 3