Define set operation a * b = {Z Z = XY, X ∈ a, X ∈ B}, set a = {1,2}, B = {0,2}, then the sum of all elements of set a * B is A0 B2 C3 D6 The book says that the answer is D, but only 0, 2 and 4 are calculated. How can I choose D

A*B={0,2,4}
0+2+4=6
Choose D

How to prove the definite integral whose absolute value is less than or equal to the absolute value of integrand

-|F (T) | f (T) | f (T) | integral on both sides:
- ∫|f(t)|dt《 ∫f(t)dt《 ∫|f(t)|dt
That is: | f (T) DT | f (T) | DT

Which two identical numbers multiply by 5? Which two identical numbers multiply by 80?
Are there any specific numbers? I don't understand the root number

(±√5）^2=5
(±4√5)^2=80
Add: specific number has pull
However, the calculation is infinite non cyclic decimal, can not have an accurate value
So it's usually indicated by the change sign
But you haven't learned me yet
I can only tell you:
For example, the 4-switch sign is plus or minus 2, and the 16 switch sign is plus or minus 4
More detailed can only be explained to you by your teacher

Sixth grade math problems (formula should also be written)
Master Zhang uses tin sheet to make 10 cylindrical ventilation pipes (diameter: 0.2m, height: 1m). How many square meters of tin sheet should he use at least? (the joint part is ignored)
[[process also needs to be written]]

[interpretation]
0.2×3.14×1×10
=6.28 (M2)
A: at least 6.28 square meters of white iron sheet should be used
Calculate perimeter with diameter, multiply by 1 meter, it is the side area of one section of air duct, multiply by 10, it is the iron sheet area of 10 sections of air duct

How many natural numbers can be made up of 1, 2, 3, 4 and 5
Such as the problem! To you to solve. Thank you In a hurry

A(1,5)＋A(2,5)＋A(3,5)＋A(4,5)＋A(5,5)
=5＋20＋60＋120＋120
=325

F (x) is a even function defined on R, and f (2-x) = f (2 + x) is r constant for X. it is proved that f (x) is a periodic function

If f (x) is an even function defined on R, then f (- x) = f (x)
So, f (2-x) = f (X-2)
And because f (2-x) = f (2 + x)
So: F (X-2) = f (x + 2)
That is: F [(x + 2) - 2] = f [(x + 2) + 2]
We get: F (x) = f (x + 4)
So, f (x) is a periodic function, t = 4

Xiaoling wants to put the 18cm long pencil into a 15cm long, 4cm wide and 3cm high carton. She asks: can the carton be covered after the pencil is put into the carton? If yes, please explain why; if not, how long can this box hold at most?

According to the meaning of the title: ac2 = AB2 + BC2, AC'2 = ac2 + CC'2, so AC'2 = AB2 + BC2 + CC'2, so the diagonal length AC'152 + 42 + 32 = 510 (CM), ∫ 510 < 18, ∫ can't be covered, so this box can hold 510cm pencil at most

What are the center and center of gravity of the triangle?

The five centers of a triangle
A theorem
Theorem of center of gravity: the three central lines of a triangle intersect at a point, which is the point to the vertex
It's twice the distance from it to the midpoint of the opposite side. This point is called the center of gravity of the triangle
Outer center theorem: the vertical bisectors of the three sides of a triangle meet at a point. This point is called the outer center of the triangle
Perpendicularity theorem: the three heights of a triangle intersect at a point. This point is called the perpendicularity of a triangle
Inner theorem: the bisectors of the three inner angles of a triangle meet at a point. This point is called the inner point of a triangle
Side center theorem: the bisector of an inner angle of a triangle intersects the bisector of the outer angle at the other two vertices at a point. This point is called the side center of a triangle. A triangle has three side centers
The center of gravity, outer center, perpendicular center, inner center and side center of a triangle are called the five centers of a triangle
The above-mentioned conclusions have been discovered as early as Euclid's time. Except for the perpendicular theorem, Euclid collected them as important theorems in his original geometry. However, many studies on the triangle and many famous conclusions show that the omission of the perpendicular theorem is an oversight of the author of the original geometry

The solution of inequality 12x ax > a about X

12x-ax-a ＞ 0 is transformed into the following form (3x-a) (4x + a) ＞ 0 by cross phase multiplication. The two solutions of equation (3x-a) (4x + a) = 0 are (a third of a) or (a negative quarter of a). The following discussion is carried out: 1. When a ＞ 0, X is less than (a negative quarter of a) and greater than (a third of a) 2. When a is less than 0, X is less than (a third of a) and greater than (a negative quarter of a) 3, For inequalities with parameters, the most important thing is to classify them

Define set operation a * b = {Z Z = XY, X ∈ a, X ∈ B}, set a = {1,2}, B = {0,2}, then the sum of all elements of set a * B is A0 B2 C3 D6 The book says that the answer is D, but only 0, 2 and 4 are calculated. How can I choose D