Given DZ = 5xdx + Y & # 710; 2dy, find δ & # 710; 2Z / δ y δ x, (second order mixed partial derivative), and δ is the sign of partial derivative

Given DZ = 5xdx + Y & # 710; 2dy, find δ & # 710; 2Z / δ y δ x, (second order mixed partial derivative), and δ is the sign of partial derivative

Because DZ = 5xdx + y (dxdx + y) is a dxdxdx + y (DX = 5 x DX + y, and the coefficient y of Dy, so the coefficient y of Dy, y # 178; y, the coefficient y \35, y \# 178; y, the coefficient y \35; y \#; y, the coefficient y \\\\\\; y, then, then, then \\\\\\\\\\\\\\\\\\\\\x = 0

Finding total differential u = e ^ XYZ

du/dx=yze^(xyz),du/dy=xze^(xyz),du/dz=xye^(xyz)
du=yze^(xyz)dx+xze^(xyz)dy+xye^(xyz)dz

Brothers and sisters help little sister,
Xiao Ming's grandfather went to the vegetable market to buy vegetables. After walking 450 meters, grandma found that his grandfather didn't bring the basket and asked him to send it. Xiao Ming caught up with his grandfather in 15 minutes. At this time, his grandfather also found that he didn't bring the basket and returned immediately. Xiao Ming and his grandfather can meet in three minutes. What's the speed of each of them?
Thank you first, little sister

The equations are better
Let the speed of grandfather and Xiao Ming be XM / min and YM / min respectively
{15x+450=15y
3x+3y=450
x=60,y=90

General term formula of sequence 1 / 2 3 / 4 5 / 8 11 / 16

General term formula of sequence 1 / 2 3 / 4 5 / 8 11 / 16
The sequence satisfies the recursive formula: an + a (n-1) / 2 = 1, and A1 = 1 / 2
That is, 2An = - A (n-1) + 2, that is, 2 (An-2 / 3) = - (a (n-1) - 2 / 3)
Thus {(An-2 / 3)} is an equal ratio sequence with the first term A1-2 / 3 = - 1 / 6 and the common ratio - 1 / 2
An-2/3=(-1/3)(-1/2)^n
An=(2^(n+1)-(-1)^n)/(3*2^n)

If 100x = 4100y = 9, then 102x + 2Y=______ ．

100x = 102x = 4100y = 102y = 9102x + 2Y = 102x × 102y = 4 × 9 = 36, so the answer is: 36

Engineering problems of linear equation with one variable
1. It takes 11 days for Party A to dig a 1210 meter long canal, while it takes 20 days for Party B to do it alone. Now Party A and Party B are working at the same time. How many days is it estimated to take to dig this canal?
2. To build a highway, it takes 80 days for Party A to contract alone, and 120 days for Party B to contract alone. 1) how many days can it be completed by two engineering teams now? 2) if Party A and Party B have cooperated for 30 days, and because Party A has other tasks, the remaining work will be completed by Party B, how many days will it take to build the highway?
3. A pool can be filled with three water pipes, i.e. pipe a can be filled in 10 hours, pipe B can be filled in 15 hours, and pipe C can be filled in 20 hours. Now the three pipes are all opened, and pipe a is closed halfway. As a result, the pool is filled in 6 hours. How many hours has pipe a been actually opened?
(solving problems with equations)

1. It is estimated that it will take X days to complete the excavation of this canal. Analysis: a completes 1210 / 11 meters a day, B completes 1210 / 20 meters a day, and now Party A and Party B construct at the same time, their daily completion is: (1210 / 11 + 1210 / 20) meters

If you arrange natural numbers as follows, what are the rows and columns of 2005
1 2 4 7 11 16 ...
3 5 8 12 17 ......
6 9 13 18 .........
10 14 19 ............
15 20 ...............
21 ..................
.....................

Look at the first column number 1 = 13 = 1 + 26 = 1 + 2 + 3 21 = 1 + 2 + 3 + 4 + 5 + 6, then the first column in row n = 1 + 2 + 3 + N = (n + 1) n / 2 obviously there is (n + 1) n / 2 ≤ 2005 ≤ (n + 2) (n + 1) / 2, then when n = 62, the first line becomes immediately, and the 63rd column is 62 * 63 / 2 + 1 = 1954, 2005-1954 = 512005

Root 2A multiplied by the square of root 3 (b) divided by the cube of root 9 (b)

Unit 1-6 English phrases
There should be sentences and phrases. School will start soon

UNIT 11. how often 2. on weekends 3. hardly ever 4. twice a week ...

There are 160 red, yellow and white balls. If you take out 13 red balls, 14 yellow balls and 15 white balls, there are 120 left. If you take out 15 red balls, 14 yellow balls and 13 white balls, there are 116 left. How many red, yellow and white balls are there?

According to the above analysis, taking 160 △ 40 = 4 times just finished, red ball is still poor: 43-1 = 13, white ball is more than 1-45 = 15, yellow ball is finished; it shows that 13 of red ball is equal to 15 of white ball, the ratio of red ball to white ball is 3:5; according to the comparison of two schemes, it is found that 13-15 = 215 of white ball is more than 215 of red ball by 4; that is, white ball is more than red ball by 4 △ 215 = 30, so red ball has 30 △ 215（ 5-3) × 3 = 45; white ball has 45 + 30 = 75; yellow ball is 160-45-75 = 40; answer: (1) original yellow ball 40, (2) original red ball 45, white ball 75