On the concept of higher numbers If FX is bounded in a neighborhood, what is the condition for FX to have a limit at XO

On the concept of higher numbers If FX is bounded in a neighborhood, what is the condition for FX to have a limit at XO

Science. Find a solid metal ball, use a spring dynamometer to measure the gravity in the air of 54 n, immerse it in water, spring
Find a solid metal ball, use a spring dynamometer to measure 54 n outside the gravity in the air, immerse it in water, the test number of spring scale is 34 n, find g = 10N / kg
(1) How buoyant is the metal ball?
(2) What is the volume of the metal ball in cubic meters
(3) What is the metal composition of the ball

Buoyancy = gravity in air - Indication in water = 54n-34n = 20n
Because of immersion, the volume of the object = the volume of the discharged water = 20 / 10 / 1000 = 0.002m & sup3;
According to gravity, the mass m = g / g = 54 / 10 = 5.4kg, density M / v = 5.4kg/0.002m & sup3; = 2.7 * 1000kg / M & sup3;, the material is aluminum

The bottom area of a rectangle is a square with a side length of x cm, the height is 1 cm, and the volume of a rectangle is y cm. Find the functional relationship between Y and X

Y = x squared

Two objects with mass M1 = 2kg / m2 = 4kg are stacked on a smooth horizontal surface, and the friction coefficient is 0.2
At present, a force increasing with time t is applied to an object with mass m2. The relationship between F and time is f = 3 + 12t. Ball: the relationship between A1 and A2 and time T. note: M1 is below

Since the horizontal plane is smooth, M1 slides with m2 at the beginning. Let F1 be the maximum friction between M2 and M1, F1 = um2g = 0.2 * 4 * 10 = 8N
When f is less than or equal to F1, the position relationship of A1A2 remains unchanged, f = F1 = 3 + 12t = 8, t = 4.17s. Then, with the increase of T, f increases, and M2 accelerates with the acceleration of zero initial velocity relative to M1. When M2 is separated from M1, the acceleration of M2 increases suddenly

The growth rate is negative,
In August 2011, the total value of China's foreign trade import and export was 191.7 billion yuan, a 4.3% decline on a month on month basis?
The answer is = 1917 / (1-4.3%) and then multiply by 4.3%, resulting in 8.6 billion
But if the growth rate is - 4.3%, why is it multiplied by a positive number?

1917 / (1-4.3%). The result is the total value of foreign trade imports and exports in 2010, which decreased by 4.3% on a month on month basis. That is to say, the total value of foreign trade imports and exports in 2010 decreased by 4.3%. The result is the value of decline. You can also think of it as negative or positive, with a decrease of - 8.6 billion. Isn't that an increase of 8.6 billion?

There is an object block with mass m on the horizontal turntable, the length of the rope connecting the object block and the rotating shaft is r, the maximum static friction between the object block and the turntable is μ times of the pressure, and the angular velocity of the turntable increases gradually from zero. When the angular velocity is μ g / 2R under the root sign and 3 μ g / 2R under the root sign respectively, the tensile force of the rope on the object block is calculated

Centripetal force F = w ^ 2 * r, the first pulling force is 0, and the second pulling force is 2umg

In the arithmetic sequence an, A3 = A9 = 27-a6, Sn is the sum of the first n terms of the sequence an, then S11=

Arithmetic sequence an = an-1 + M
An = A0 + mn
A9-A3=0=6m
So m = 0
That is, an = am
A9=27-A6
2*A9=27
A9=13.5
S11=A1+A2+...+A11=11*A9=11*13.5=148.5

There are two cars a and B on the straight road. A starts to drive from a standstill at an acceleration of 0.5m/s2, and B moves at a constant speed in the same direction at a speed of 5m / s 200m in front of A. question: (1) when will a catch up with B? How fast does a catch up with B? How far is a from the starting point? (2) In the process of catching up, when is the maximum distance between a and B? What is the distance?

(1) When a overtakes B, the difference of their displacements is x0 = 200m, & nbsp; x a = x0 + X B. let a overtake B with time t, then x a = 12a a T2, x B = v b T. according to the condition of overtaking, there is 12a T2 = v b t + 200, and the solution is t = 40 & nbsp; s or T = - 20 & nbsp; s (rounding off). Then the velocity of a is v a = a T = 0.5 × 40 & nbsp; m / S = 20 & nbsp; s; M / s, x a = 12a, T2 = 12 × 0.5 × 402 & nbsp; m = 400 & nbsp; m. (2) in the process of catching up, when a's speed is less than B's, the distance between a and B is still increasing, but when a's speed is greater than B's, the distance between a and b decreases. When the two speeds are equal, the distance between a and B reaches the maximum. From a a T = v b, t = 10 & nbsp; s, that is, a is at 10 & nbsp; s; Xmax = x0 + V B t-12a a T2 = (200 + 5 × 10-12 × 0.5 × 102) & nbsp; m = 225 & nbsp; M. (1) a catches up with B in 40s, and the speed of a catches up with B is 20 & nbsp; m / s, at this time a is 400 & nbsp; m from the starting point. (2) in the process of catching up, there is a maximum distance between a and B at 10 & nbsp; s, which is 225 & nbsp; M

Xiao Gang and Xiao Ming practice running together. Xiao Gang takes five minutes to make a circle. Xiao Ming takes four minutes to start at the same time. How many minutes does it take at least for them to meet at the starting point

20 minutes

The equation 2A + 5 / 3 = 5AX + 1 / 4 (2a + 5 and 5AX + 1 are both above the fractional line), X is negative, then the value range of a is?
At the beginning, I calculated a ＜ - 17 / 8 (eight out of seventeen). When I checked, I took the value of - 4 and substituted it into the original formula. I found that X was not a negative number. Then I recalculated, and the result was still a ＜ - 17 / 8, which was not correct. Finally, I found that the correct answer was a ＞ - 17 / 8, but no matter what the original formula was, I could not get the correct answer,

If the denominator of the original formula is removed, 8A + 20 = 15ax + 3 -------- 8A + 17 = 15ax,
So x = (8a + 17) / (15a)
Because x is negative, so = (8a + 17) / (15a) < 0
There are two cases: (1) 8A + 17 > 0
15a