The newly built teaching building needs 150 cuboid drainage pipes with a length of 3 meters, a width of 1 decimeter and a height of 8 cm. The surface of the drainage pipe is a layer of iron sheet, which needs iron sheet How many square meters?

1 decimeter = 0.1 meter 8 cm = 0.08 meter
Area of iron sheet required for one drainage pipe = (0.1 + 0.08) × 2 × 3 = 1.08 (M2)
Total required iron sheet area = 1.08 × 150 = 162 (M2)

A kind of cuboid water pipe, 40 decimeters long, 15 cm wide, 8 cm high. How many decimeters of iron sheet is needed to make 20 sections at least?

40 times 15 = 600
40 times 8 = 320
600+320=920
920 times 20 = 18400
18400cm=1840dm

Log10 (1 + 1 / 7) = a, log10 (1 + 1 / 49) = B, try a, B means LG2, lg7

Log10 (1 + 1 / 7) = a, lg8-lg7 = a, 3lg2-lg7 = alg10 (1 + 1 / 49) = B, lg50-lg49 = B, lg100-lg2-2lg7 = B, LG2 + 2lg7 = 2-B, so 7lg2 = 2A + 2-B, LG2 = (2a + 2-7) / 77lg7 = 3 (2-B) - a = 6-3b-a, lg7 = (6-3b-a) / 7

Whether there is a real number α such that sin α - cos α = 7 / 5

There is a real number α such that sin α - cos α = 7 / 5
As long as sin α = 4 / 5, cos α = - 3 / 5
Or, sin α = 5, cos α = - 47 / 5

1. Xiaoqing and Xiaoliang read the same book, Xiaoqing read 12 pages a day, Xiaoliang read 8 pages a day, after how many days Xiaoqing coin Xiaoliang read 68 pages more?
2. Xiao Ming and Xiao Hua practice running on a 400 meter circular track. They start from the same point and go in the same direction at the same time. Xiao Ming runs 3.5 meters per second and Xiao Hua runs 5.5 meters per second. After how many seconds, they meet for the first time

1. Set X days, Xiaoqing read 68 pages more than Xiaoliang
(12-8)x=68
x=17
Explanation: 12-8 is the number of pages you read every day
2. We met in x seconds
(5.5-3.5)x=400
x=200
Explanation: Xiaohua ran 400 meters more than Xiaoliang when he first met

Finding the derivative of piecewise function
Let g (x) / x = 0
f(x)={ 0 x=0 g(0)=g'(0)=0 g"(0)=2
Find f '(0)

f(x)=g(x)/x,x!=0;f(x)=o,x=0
The Taylor expansion of G (x) in x = 0 is g (x) = g (0) + G '(0) x + G "(0) x ^ 2 / 2! + O (x ^ 2)
f'(0)=lim(x->0)[(f(x)-f(0))/(x-0)]
=lim(x->0)f(x)/x
=lim(x->0)g(x)/x^2
=lim(x->0)[g(0)+g'(0)x+g"(0)x^2/2!+O(x^2)] /x^2
Substituting g (0) = g '(0) = 0, G "(0) = 2,
=1

Given a > 1, b > 1, C > 1, compare the size of ABC + A + B + C and ab + BC + Ca + 1
Such as the title

(abc+a+b+c)-(ab+bc+ca+1)……………… (difference method)
=abc-ab-bc-ca+a+b+c-1……………… (factorization)
=(a-1)(b-1)(c-1)>0 ……………… (according to a > 1, b > 1, C > 1,)
So ABC + A + B + C > AB + BC + Ca + 1

In special relativity, the combined speed of any object passing through time and space is always exactly equal to the speed of light
What is the basis of Einstein's conclusion? And why is the combination of speed not the harmony? What is the meaning of the combination? (I don't know if the book is misprinted.)

LZ seems to have the wrong number. It should be through space and time, not time and space
I understand that
When there is no external force (no acceleration), the speed of all objects passing through "space-time" is the same (including light),
Time and space are space and time
But because the speed through space is relative, there is no absolute moving speed
If an object doesn't move and its speed through space is 0, then its speed through time is light speed and time passes normally
If an object is set as the speed of light and its speed through space is C = the speed of light, then its speed through time is 0 and time stops
If the speed of an object is lower than the speed of light, the speed through space V, 0

Calculation: (3x + 1) ^ 2 (3x-1) ^ 2 - (2x + 1) (- 2x + 1)

Original formula = (3x + 1) ^ 2 (3x-1) ^ 2 + (2x + 1) (2x-1)
=(3x+1)^2 (3x-1)^2+4x^2-1
=(9x^2+1+6x)(9x^2+1-6x)+4x^2-1
=81x^4-54x^3+9x^2+9x^2-6x+1+54x^3-36x^2+6x+4x^2-1
=81x^4-14x^2

The circumference of a rectangle is 26cm. If the length of the rectangle is reduced by 1cm and the width is increased by 2cm, it will become a square. If the length of the rectangle is xcm, the equation ()
A. x-1=（26-x）+2B. x-1=（13-x）+2C. x+1=（26-x）-2D. x+1=（13-x）-2

Let the length of the rectangle be xcm, then the width is (13-x) cm. According to the equivalent relation: the length of the rectangle - 1cm = the width of the rectangle + 2cm, the equation is: X-1 = (13-x) + 2, so choose B

The newly built teaching building needs 150 cuboid drainage pipes with a length of 3 meters, a width of 1 decimeter and a height of 8 cm. The surface of the drainage pipe is a layer of iron sheet, which needs iron sheet How many square meters?