According to the equation, there are 3200 RMB in denomination of 1.5 yuan and 10 yuan. The number of the three kinds of RMB is the same

According to the equation, there are 3200 RMB in denomination of 1.5 yuan and 10 yuan. The number of the three kinds of RMB is the same

There are x pieces of RMB each
（1＋5＋10）X＝3200
16X＝3200
X＝200

Xiaodong's mother received a bonus of 424 yuan from her unit, of which 80 were 2 yuan, 5 yuan and 10 yuan, and the number of 5 yuan and 10 yuan were equal,
How many of these three kinds of RMB

Suppose 5 yuan is x, then 10 yuan is x, 2 yuan is 80-2x
Then: (80-2x) x2 + 5x + 10x = 424
X = 24 sheets
So: 32 for 2 yuan, 24 for 5 yuan and 24 for 10 yuan

X is a rational number, find the minimum value of | x-2007 | + | x + 2008 |

|The minimum value of x-2007 | + | x + 2008 |
(1)x>=2007
|x-2007|+|x+2008|
=x-2007+x+2008
=2x+1
The minimum value of the original formula is 4015
(2)-2008

How to solve the equation 16.5 times 8-12.4x = 51.4

16.5 times 8-12.4x = 51.4
16.5 times 8-51.4 = 12.4x
x=6.5

Elephant: my weight is 5 tons, whale: I'm 25 times less than the elephant's weight by 1 ton. How many tons does the whale weigh?
How many oranges are there in each box? How many oranges do you plan to eat?
(equation must be used)
The second question is to buy back a box of oranges. I have the wrong number

The weight of a whale is x tons
25x-1=5
x=124
A:···
There are x oranges in each box
（x-48）/4=（x+8）/6
x=160
(160-48) / 4 = 28
A:····

Let f (x) satisfy f (x + y) = f (x) + F (y) + 4xy (x, y ∈ R) and f '(1) = 2, then the root of the equation f' (x) = 0 is
In the beginning, how can we get f '(x + y) = f' (x) + 4Y?
Y has nothing to do with X, and is not a function of X. for X, f '(x + y) = f' (x) + 4Y
X = 1, f '(1 + y) = f' (1) + 4Y = 2 + 4Y
Let 1 + y = t, then y = T-1; Let f '(T) = 2 + 4 (t-1) = 4t-2
f'（t)=4t-2=0
t=1/2
The derivative of F (x) is 0 and the root is 1 / 2
I think so. At the beginning, is this the way to find the derivation?
f（x+y）=f（x）+f（y）+4xy
f'(x+y) (x+y)'=f'(x)+f'(y)*y'+4(xy)'
f'(x+y) (x'+y')=f'(x)+f'(y)*y'+4(x'*y+x*y')

If x is a derivative of X, and X and y are not related, that is to say, for X, y is a constant
F '(x + y) = f' (x) + [f (y)] '+ (4Y * x)' (note that this is for the derivation of X, y is a constant, and f (y) is also a constant)
=f’（x）+0+4y

Principles of computer English abbreviation
For example, there are some commands to quickly open the page, such as: compmgmt.msc (computer management ) secpol.msc (Security Policy). I know the full English names of some abbreviations. I mainly want to ask if there are any principles for abbreviations? For example, what kind of letter should be removed? If I know, it will be very convenient to remember the command later!

No, you think too much

R1: R2 = 1:4; why r total = r1r2 / R1 + R2 = R2 / 5

Because it's parallel. Parallel is 1 / R1 + 1 / r2 = 1 / R. the total deformation is one

Expand the binomial (1-2x) ^ 5 to get the coefficient of x ^ 3

Solving binomial (1-2x) ^ 5 expansion with x ^ 3 terms
It is C (5,3) 1 ^ 2 (- 2x) ^ 3
=C(5,3)(-2x）^3
=(-2)^3C(5,3)(x）^3
=-8*10(x）^3
=-80x³
The coefficient of x ^ 3 is - 80

A + B = 5, A-B = 3, then what is the value of AB?

a+b=5
a-b=3
a=4
b=1
ab=4