Let L and m be two non perpendicular straight lines with different surfaces, and try to prove that the surface generated by the rotation of the straight line m around the straight line L is a hyperboloid with one sheet

Let L and m be two non perpendicular straight lines with different surfaces, and try to prove that the surface generated by the rotation of the straight line m around the straight line L is a hyperboloid with one sheet

Its exact name is "univalent hyperboloid". Every horizontal section is an ellipse. But yours is a special case. The denominator's B = a. the section is a circle. From the longitudinal direction of the graph, every boundary section is a hyperbola. As you said, don't look at it as a "surface", it can be composed of straight lines (as generatrix)
This is part of the "surface" of space analytic geometry

Will zero degree ice melt in zero degree water

Only when there is a temperature difference between the two can heat transfer occur and the ice will melt
There is no temperature difference between the two

In Niu 2, why - F = ma?

Acceleration is directly proportional to force and inversely proportional to mass

Proving problem. Proving (1-1 / 3) (1-1 / 3 ^ 2) (1-1 / 3 ^ 3) ×. (1-1 / 3 ^ n) > 1 / 2

(1-1 / 3) (1-1 / 3 ^ 2) = 1-1 / 3 - (1-1 / 3) * 1 / 3 ^ 2 > 1-1 / 3-1 * 1 / 3 ^ 2 = 1-1 / 3-1 / 3 ^ 2. Similarly, n times of processing, we get (1-1 / 3) (1-1 / 3 ^ 2) (1-1 / 3 ^ 3) (1-3^n)>1 - 1/3 - 1/3^2 - 1/3^3 … - 1/3^n=2 - ( 1 + 1/3 + 1/3^2 + 1/3^3 … + 1/3^n )=2 - 1/(1 - 1/3) + 1/3^(n+1)=2 - 3/2 + 1/3^(n+1)=1/2 + 1/3^(n+1)>1/2
Lazy to write, baidu direct, old topic

Among the following locations, the one that meets the three conditions of eastern hemisphere, Northern Hemisphere and low latitude is ()
A. 21 ° W, 0 ° B, 0 ° n, 26 ° C, 165 ° e, 17 ° D, 19 ° W, 15 ° s

According to the analysis of the four options in the question stem, point a is located on the boundary line of the Western Hemisphere, low latitude and Northern and southern hemisphere, point B is located in the eastern hemisphere, Northern Hemisphere and low latitude, point C is located in the Western Hemisphere, Northern Hemisphere and low latitude, and point D is located in the eastern hemisphere, southern hemisphere and low latitude

Given that the sum of three consecutive odd numbers is 15 more than the sum of two even numbers between them, find the three consecutive odd numbers

3x-2x=15
x=15
Then the three consecutive odd numbers are 13, 15 and 17

Let a be a real root of the equation x ^ 2 + x-2011 = 0, then the value of a ^ 2 + a-2011 needs detailed process

Because a is a real root of the equation x ^ 2 + x-2011 = 0, it is directly substituted into a ^ 2 + a-2011 = 0

The ninth power of (- 130), the seventh power of 105, the third power of (- 38.9) of 8.53

(- 130) - 10604499373000000
The seventh power of 105: 140710042265625
The third power of 8.53 is 620.650477
The third power of (- 38.9) -58863.869

Calculate the square of 99.8 skillfully
Clever calculation:
99.8 square
19.8 times 20.2

99.8*99.8=(100-0.2)(100-0.2)
=100*100-2*0.2*100+0.2*0.2
=10000-40+0.04
=9960.04
（a-b）(a-b)=a*a-2ab+b*b
19.8*20.2=（20-0.2)(20+0.2）
=20*20-0.2*0.2
=400-0.04
=399.96
(a-b)(a+b)=a*a-b*b
Simple mathematical formula

Let y = ax + 2A + 1, when - 1 ≤ x ≤ 1, the value of Y has positive and negative, then the value range of the real number a___ ．

∵ function y = f (x) = ax + 2A + 1, when - 1 ≤ x ≤ 1, the value of Y has positive and negative, ∵ f (- 1) f (1) < 0, that is (- A + 2A + 1) (a + 2A + 1) < 0, ∵ (a + 1) (3a + 1) < 0, the solution is - 1 < a < 113; ∵ the value range of real number a is (- 1, - 13). So the answer is: (- 1, - 13)