Engel's coefficient (denoted as n) is commonly used to measure the living standard of people in a country or region in the world. Its calculation formula is: n = family day

Engel's coefficient (denoted as n) is commonly used to measure the living standard of people in a country or region in the world. Its calculation formula is: n = family day

The ratio reflects the living standard of residents

Easy operation!)
1. Minus one and 4 / 7 times one and 4 / 7 divided by (minus one minus 4 / 7) plus one and 4 / 7
2. One and another 1 / 2 times [3 times (minus 2 / 3) Square-1] - (1-2 / 3) times (- 2) cube
3. (1 / 2 + 2 / 3 + 3 / 4 +. + 2011 / 2012) times (1 + 1 / 2 + 2 / 3 +... + 2010 / 2011) minus (1 / 2 + 2 / 3 +... + 2011 / 2012) times (1 / 2 + 2 / 3 +... + 2010 / 2011)

1, negative 1-4 / 7 is the same as 1 and 4 / 7, - 11 / 7 * 11 / 7 divided by 11 / 7 + 11 / 7 = 11 / 7 + 11 / 7 = 3 and 1 / 7
2 = 3 / 2 * (3 * 4 / 9-1) - 1 / 3 * 2 ^ 3 = 3 / 2 * 1 / 3-8 / 3 = 1 / 2-8 / 3 = - 2 and 1 / 6
3 = let (1 / 2 + 2 / 3 +...) +2010 / 2011) = a, set this paragraph as a to be intuitive and easy to understand
=（a+2011/2012)*(1+a)-(1+a+2011/2012)*a=a*(1+a)+2011/2012*(1+a)-(1+a)*a-2011/2012*a
=2011/2012

2 mathematical calculation problems, requiring simple operation
① 1 / 3 * 4 + 1 / 4 * 5 +. + 1 / 29 * 30 (simple operation)
② 1 / 2 + 1 / 6 + 1 / 30 (simple operation)

1、1/（3×4）+1/（4×5）+.+1/（29×30）
=1/3-1/4+1/4-1/5+.+1/29-1/30
=1/3-1/30
=3/10
2、1/2+1/6+1/20+1/30
=1-1/2+1/2-1/3+1/4-1/5+1/5-1/6
=1-1/3+1/4-1/6
=1-1/3+1/4-(1/2-1/3)
=1/2+1/4
=3/4

What do the letters on the steel bars mean?
Identification on reinforcement:
3YHG12
405H20
3CW16
4EKG16
I know that the latter two are the diameters of steel bars, but what does the former mean?
Trouble master guidance!
What grade of steel is the steel bar?

The first number on the steel bar represents the grade of steel bar, for example, 3 represents grade 2 steel, 4 represents grade 3 steel, and 5 represents grade 4 steel. It is explained in detail in the steel bar standard GB 1499.2-2007 implemented on March 1, 2008. The last two numbers represent the specification of steel bar, and the letters between the grade and specification represent the manufacturer of steel bar

What do the steel bar symbols in the concrete structure drawings mean, such as b t n g l

B = bottom reinforcement
T = top bar
N twisted waist tendon
G structure waist tendon
L lacing
Y should be Y-direction reinforcement

Solve this problem with fractional factor: A ^ 2 (B-C) + B ^ 2 (C-A) + C ^ 2 (a-b)

a^2(b-c)+b^2(c-a)+c^2(a-b)
=a^2(b-c)+cb^2-ab^2+ac^2-bc^2
=a^2(b-c)+cb(b-c)-a(b-c)(b+c)
=(b-c)(a^2+cb-ab-ac)
=(b-c)(a-c)(a-b)
That's it.

How to calculate the negative power of 2 (x + 1) = 3 (X-2),

2/（x+1）=3/（x-2）
2x-4=3x+3
-x=7
x=-7

Given that 3x-4y-z = 0, 2x + y-8z = 0, then the algebraic formula x2 + Y2 + z2xy + YZ + 2zx=______ ．

∵ 3x-4y-z = 0, ∵ z = 3x-4y, substituting 2x + y-8z = 0 to get y = 23x, substituting it into Z = 3x-4y to get z = 13X, ∵ algebraic formula x2 + Y2 + z2xy + YZ + 2zx = x2 + 49x2 + 19x2 & nbsp; & nbsp; X · 23x + 23x · 13X + 2x · 13X & nbsp; = 1

4/(a²-1)-2/(a²+a)
(1/x³-1/x²+1/x)*x³

4/(a^2-1)-2/(a^2+a) =4/(a-1)(a+1)-2/a(a+1) =[4a-2(a-1)]/[a(a-1)(a+1)]=(4a-2a+2)/[a(a-1)(a+1)]=(2a+2)/[a(a-1)(a+1)]=2(a+1)/[a(a-1)(a+1)]=2/[a(a-1)](1/x^3-1/x^2+1/x)*x^3=1-x+x^2

Find a problem of solving equation in the second fraction of junior high school!
With fractional line
Make sure you have a fraction line
Just one
With a fraction line! Don't be like this: 1 / 2x = 2 / x + 3

2 3
---=---
x-3 x