It is known that a = {y | y = 1 - | x |, X belongs to R}, B = {y | y = the square of X, X belongs to R}, the intersection of a and B is equal to?

It is known that a = {y | y = 1 - | x |, X belongs to R}, B = {y | y = the square of X, X belongs to R}, the intersection of a and B is equal to?

Because x belongs to R
So, 1 - | x | = 0
So, set a = {y | y = 0},
So, a intersects B = {y | 0

Let x, y ∈ R, then x is greater than or equal to 2 and Y is greater than or equal to 2 if the square of x ^ 2 + y is greater than or equal to 4
Let X and Y belong to R, then x is greater than or equal to 2 and Y is greater than or equal to 2 is the square of X + what is the condition that the square of Y is greater than or equal to 4?

Because x ≥ 2, y ≥ 2 can deduce x ^ 2 + y ^ 2 ≥ 4, so this is a sufficient condition
Because x ^ 2 + y ^ 2 ≥ 4 can not deduce x ≥ 2, y ≥ 2 (for example, when x ≤ - 2, y ≤ - 2, there is also x ^ 2 + y ^ 2 ≥ 4), so this is not a necessary condition
In conclusion, X ≥ 2 and Y ≥ 2 are sufficient and unnecessary conditions for x ^ 2 + y ^ 2 ≥ 4

What's the difference between the average rate and the instantaneous rate?
I'm stupid --

In physics, velocity is vector. It has direction. Average velocity = displacement / time
Instantaneous velocity = displacement / time
Average speed = distance / time
Instantaneous rate = distance / time (also very short time)
The difference between instantaneous velocity and instantaneous velocity is that one has direction and the other has no direction
The difference between speed and speed is that there are trees and directions
Do you need to say the difference between distance and displacement

The diameter of the bottom of the cone is 80 cm, and the length of the generatrix is 90 cm. Find the central angle of the expanded side view of the cone
The arc circumference / generatrix of the center angle is equal to 80 π / 90. Is this formula finished? So the center angle is more than 2 degrees

The generatrix is the radius of the expanded sector. Because the diameter of the cone ground is 80 cm, the arc length is 80 π, and the circumference of the circle where the sector is located is 180 π, so the center angle of the circle is 80 π / 180 π * 360 ° = 160 °

Fill in the blanks with the correct answers in brackets
A. Exaggeration B. eloquence C. evasion D. nonsense
E. Few words
Talk about ()
To say () evasively, to say () with laughter, to say ()
The groundless saying of (?) does not conform to the actual saying of (?)
Hee hee-

To speak freely (B. to be eloquent) to speak seldom (e. to be reticent)
Evasive (C. evasive) laughter accompanied by (F. laughing)
Groundless saying (D. nonsense) does not conform to the actual saying (A. exaggeration)

If the circumference of the big and small circles is 3:2, the area of the big circle is () more than that of the small circle

The radius of the big circle is r, and the radius of the small circle is R2R * 3.14: 2R * 3.14 = R: r = 3:2, that is, R / r = 3 / 2 (R * r * 3.14-r * r * 3.14) / R * r * 3.14) * 100% = [(R * r) / (R * r) - 1] * 100% = [(3 / 2) (3 / 2) - 1] * 100% = 5 / 4 * 100% = 125%. The area of the big circle is 125% larger than that of the small circle

It is known that the sides of a triangular prism are all rectangles. To prove, the area of any two sides of a triangular prism is larger than that of the third side

It is known that all sides of a triangular prism are rectangles, and the opposite sides of the rectangles are equal
The top and bottom of a triangular prism are equal and are triangles
The sum of any two sides of a triangle is greater than the third side: a + b > C, ｜ ah + BH > CH (h -- high)
The area of any two sides is larger than that of the third

Knowing the chord length and chord height of an arc length, how to calculate the arc length?

Ask: know the chord length L and chord height h of an arc length, how to calculate the arc length C? The arc radius is r, and the center angle of the arc is A.R ^ 2 = (R-H) ^ 2 + (L / 2) ^ 2R ^ 2 = R ^ 2-2 * r * H + H ^ 2 + L ^ 2 / 42 * r * H = H ^ 2 + L ^ 2 / 4R = H / 2 + L ^ 2 / (8 * h) a = 2 * arc sin ((L / 2) / R) degree = (2 * arc sin ((L / 2) / R)) * pi / 180

A problem of summation
1+1/(1+2)+1/(1+2+3)+.+1/(1+2+3+4+.+n)=?

Using: 1 / (1 + 2 + 3 +. N) = 1 / [(1 + n) n / 2] = 2 / [n (n + 1)] = 2 [1 / n-1 / (n + 1)], so the original formula = 1 + 2 (1 / 2-1 / 3) + 2 (1 / 3-1 / 4) +... + 2 [1 / n-1 / (n + 1)] = 1 + 2 (1 / 2-1 / 3 + 1 / 3-1 / 4 +... + 1 / n-1 / (n + 1)) = 1 + 2 (1 / 2-1 / (n + 1)) = 1 + 1-2 / (n + 1) = 2-2 / (n + 1)

The poetic meaning of berthing a boat in Guazhou

Let's go to the fifth grade. We just learned here. The teacher's teaching materials are as follows:
Boat berthing in Guazhou: it's only a river from Jingkou to Guazhou, and it's only a few mountains from Jingkou to Nanjing. The spring breeze is blowing green on both sides of the Yangtze River. When will the moon shine on my way home?