(1) [(35 / 6-49 / 12 + 63 / 20-77 / 30-105 / 56) / 1 / 8 is the best,

(1) [(35 / 6-49 / 12 + 63 / 20-77 / 30-105 / 56) / 1 / 8 is the best,

（1）[(35/6-49/12+63/20-77/30+91/42-105/56)]/1/8 =[(5/6-7/12+9/20-11/30+13/42-15/56)×7×8=[1/2+1/3-1/3-1/4+1/4+1/5-1/5-1/6+1/6+1/6-1/7-1/8]×56=[1/2-1/8]×56=3/8×56=21

8. Matrix A = [45 12 8; 9 30 86; 21 24 3; 5 46 35] B = [- 18 23 6 97; 52 64 28 56; 4 55 6]
Calculation: 1. Calculate the dimension of two matrices respectively
② Calculate the product of two matrices

>> rank(A)
ans =
three
>> rank(B)
ans =
three
>> A*B
ans =
-154 1843 646 5085
1742 2557 1324 3069
882 2034 813 3399
2442 3234 1493 3271
>>

How many hectares is one mu?

1 mu = 1 / 15 ha

An iron ball is hung under the spring scale. The indication of the spring scale is 3.92 n
An iron ball is hung under the spring scale, and the indication of the spring scale is 3.92n. Put the iron ball in the water, and the indication of the spring scale is 2.94n, so it is necessary to calculate
(1) Buoyancy of iron ball
(2) The volume of iron ball
(3) Is the iron ball hollow or solid

First, draw the stress diagram
92 n for G and 2. 94 n for discharge
The buoyancy is 0.98n
According to the formula F = liquid density (i.e. water) * g * v
Bring in the data one by one to get the V row
Because it's completely in
So row V is iron ball v
Don't forget to answer the questions as soon as you finish
Question 2: calculate the mass with volume and density. Compare with the original mass (3.92n), if it is more than the original mass, it is hollow

The functional relation between the inner angle s (degree) of a polygon and its number of sides n is?

If the number of sides of a regular polygon is n and the degree of each inner angle is s, then the polygon can be divided into (n-2) triangles
s=(n-2)180/n

As shown in the figure, the wooden board B with mass of MB = 14kg is placed on the horizontal ground, and the wooden box a with mass of Ma = 10kg is placed on the wooden board B. one end of a light rope is tied to the wooden box, and the other end is tied to the wooden pile on the ground. When the rope is tightened, the included angle with the horizontal plane is = 37 °. It is known that the dynamic friction coefficient between wooden box a and wooden board B is μ 1 = 0.5, The dynamic friction coefficient between board B and the ground is μ 2 = 0.4. The acceleration of gravity g is taken as 10m / S2. Now the horizontal force F is used to draw board B out from the bottom of wooden box a at a constant speed, and the test results are as follows: (sin 37 ° = 0.6, cos 37 ° = 0.8)
(1) The tension t on the rope; (6 points)
(2) The size of pulling force F. (6 points)
Please explain in detail, and explain the size and direction of the tension of the rope,
When is the tension equal to the pull of a rope and when is it not?
Is the tension between the pile and a equal to the tension f? Is the tension between the stick and a equal to the tension? What's the relationship between the pull and the tension on the rope? The answer is 100N and 200N

The vertical direction of the system is in equilibrium. First, the whole system (A and b) is subjected to the component force of the tension t of the rope in the vertical direction, and the supporting force of the ground is n gravity g = 240 n, so the formula of 0.6T + 240 = n 1 is used to isolate a and B, and then a and B are respectively in equilibrium. Let f get 0.6T + 100 = f 2 from a, and 0.8t = 0.5f 3 from B

How to calculate negative multiplication?

You need to determine the symbol first
The positive example of the same sign is: (- 3) × (- 5) = + (3 × 5) = + 15
Negative example of different sign: (+ 3) × (- 5) = - (3 × 5) = - 15
If you multiply a number by 0, you still have the same number
Try to do it yourself
1、（+8）×（+5）=
2、（-8）×（-5）=
3、（+2）×（-3）=
4、（-2）×（+3）=
("+" can be omitted without "+" as "positive" sign and "-" as "negative" sign)
Answer: 1, + 40 2, + 40 3, - 6 4, - 6

Two uniform disks with mass of M and 2M and radius of R and 2R are coaxially bonded together, and can be wound around the horizontal smooth solid disk passing through the disk center and perpendicular to the disk surface
Two uniform disks with mass of M and 2M and radius of R and 2R are coaxially glued together and can rotate around the horizontal smooth fixed axis passing through the disk center and perpendicular to the disk surface. The moment of inertia to the rotating axis is 9mr2 / 2. The edges of the big and small disks are wrapped with ropes, and a weight with mass of M is hung at the bottom of the rope, as shown in the figure. Calculate the angular acceleration of the disk

Let the sum of the first n terms of the arithmetic sequence {an} be Sn, S4 ≤ 4, S5 greater than or equal to 15, then the minimum value of A4 is?
2. Let an have 11 items, A1 = 0, a11 = 4, and | AK + 1-ak | = 1 (k = 1,... 10), then the number of different sequences satisfying the condition is?

S4 = 2 (a1 + A4) = 3; because 2a3-d = - 2 and because A3 > = 3, so 2A3 > = 6, so d > = 4, so A4 = A3 + d > = 7, the minimum value is 7

On a straight road, car B runs at a uniform speed of 10m / s, and car a makes a uniform deceleration movement with an initial speed of 15m / s and an acceleration of 0.5m/s2 behind car B. under what conditions can the initial distance L of the two cars make (1) the two cars do not meet each other; (2) the two cars only meet once; (3) the two cars can meet twice (assuming that the two cars do not affect each other's movement when they meet each other) ．

When the speed of two cars is equal, the time t = v a − v b a = 15 − 100.5s = 10s. At this time, the displacement of car a is x a = v a 2 − v b 22a = 225 − 1002 × 0.5m = 125m. The displacement of car B is x B = v b t = 100m. Then △ x = x A-X B = 25m, (1) l > 25m, two cars do not meet. (2) l = 25m, two cars only meet once. (3) l < 25m, two cars can meet twice. Answer: (1) l > 25m (2) l = 25m, two cars only meet once. (3) l < 25m, two cars can meet twice