X - (x / 2-40) - (x / 4 + 60) = 60

X - (x / 2-40) - (x / 4 + 60) = 60

x-(x/2-40)-(x/4+60)=60
x-x/2+40-x/4-60=60
x-x/2-x/4+40-60=60
x/4=80
x=320

【60-x】：【40+x】=1/4

【60-x】：【40+x】=1/4
40+x=4(60-x)
40+x=240-4x
5x=200
x=40

【（60-x）*40%+20%x】*40=【（40-x）*20%+4%】*60

【（60-x）*40%+20%x】*40=【（40-x）*20%+4%】*60
(24-0.4x+0.2x)X40=(8-0.2x+0.04)X60
960-8x=482.4-12x
4x=-477.6
x=-119.4

A room needs 128 pieces of square bricks with a side length of 5 decimeters. If you use square bricks with a side length of 8 decimeters, how many

Let's use x blocks
8*8*x=5*5*128
64x=3200
x=3200/64
x=50
A: it costs 50 yuan

(0.8 plus 1 / 125) multiplied by 5 / 4

(0.8 plus 1 / 125) times 5 / 4
=4 / 5 × (5 / 4) + 1 / 125 × (5 / 4)
=1 + 1 / 25 × (1 / 4)
=1 + 1 / 100
=One and one in 100
（=1.01）

If sin (3 π / 4 + α) = 5 / 13, cos (π / 4 - β) = 3 / 5, and 0 < α < π / 4 < β < 3 π / 4, the value of COS (α + β) can be obtained

∵sin（3π/4+α）=sin[(π/4+α)+π/2]=5/13
∴cos(π/4+α)=5/13
And ∵ 0 < α < π / 4 < β < 3 π / 4
∴π/4

It is known that in right triangle ABC, bdef is a square, ad = 4cm, CF = 9cm. What is the perimeter of square bdef?

Let the side length of a square be X. since the triangle CFE is similar to the triangle EDA, then 9 / x = x / 4,
We can get x square = 36, that is, x = 6, then we can get the circumference of the square as 4 times 6cm = 24cm
I hope it can help you

Non negative numbers a, B, C satisfy a + B-C = 2, A-B + 2C = 1, find the maximum and minimum of S = a + B + C
There must be a formula! It's better to have a clear explanation!

a+b=c+2
a-b=1-2c
The results show that a = (3-C) / 2, B = (3C + 1) / 2
From a, B, C > = 0 to 0

Who can change the form invariance of the first-order total differential of multivariate function in calculus? Just be more specific

Let y = f (U) and u = g (x). If u = g (x) is differentiable for X and y = f (U) is differentiable for corresponding u, then y = f [g (x)] is differentiable for X
dy = f[g(x)]’dx = f’(u)g’(x)dx = f’(u)du
We can see that whether u is a differentiable function of an independent variable or other independent variables,
The differential form dy = f '(U) Du remains unchanged
This is the form invariance of first order total differential

A rectangular vegetable field is 45 meters in circumference, 17 meters in length, and how many meters in width?
Fang Chengjie

45 △ 2-17 = 5.5m
The width is 5.5 meters