When a particle moves harmonically, the time for completing a full vibration is 10s. At a certain time, the particle passes through a certain position, and then passes through the position for 3S. Does the object pass through the position for the second time? Does the direction of velocity have the same direction? Does the displacement have the same? Does the acceleration have the same?

When a particle moves harmonically, the time for completing a full vibration is 10s. At a certain time, the particle passes through a certain position, and then passes through the position for 3S. Does the object pass through the position for the second time? Does the direction of velocity have the same direction? Does the displacement have the same? Does the acceleration have the same?

It can be seen from the figure that the displacement acceleration is the same at the same point after three passes, and the velocity movement direction is different

A rectangular cardboard, 60 cm in length and 50 cm in width. Cut out a 6 cm square from four corners and make a box
What's the surface area of this box in square centimeter, and what's its volume in liter

Length = 60-2 * 6 = 48
Width = 50-2 * 6 = 38
Height = 6
A box without a lid
Surface area = 48 * 38 + 6 * 48 * 2 + 6 * 38 * 2 = 2856 square centimeter
Volume = 38 * 48 * 6 = 10 944 CC = 10.944 L

Under what conditions are the linear velocities of two points equal?
………………………… Equal angular velocity?
My personal summary of the old forget, ask for help to write down,

By definition, linear velocity is the distance traveled per unit time, and angular velocity is the number of turns per unit time
For example:
1. Same linear speed: two points connected by the same belt, two points on the front and rear wheels of the bicycle
2. Same angular velocity: two points on the same rotating disk

The radius of the bottom of the cone is 1, and the length of the generatrix is 3. An ant starts from point B on the circumference of the bottom and climbs along the side of the cone to the midpoint of the other generatrix AC on the axial section of generatrix ab. what route does the ant follow to make the distance shortest? What's the shortest distance?

The diameter of the circle on the bottom of a cone is 2, so the circumference of the circle on the bottom is equal to 2 π. As shown in the figure, if the side of the cone is expanded to get the sector BCB ', then the ant crawls along the line BD with the shortest distance

7 () 4 () 2 = 30, mathematical symbols in brackets

7x4 +2=30

The difference between the circumference of a and B circles is 18.84cm, and the difference between their radii is () cm

The circumference difference between the two circles is 18.84 cm, and the radius difference between them is (3) cm
18.84 ﹣ 3.14 ﹣ 2 = 3cm

How to calculate the side area of a straight triangular prism
The height is 3cm, the bottom is a right triangle, the hypotenuse is 2.5cm, then 1.5cm, 2cm
Remember, there's also the surface area
And the lateral area

Surface area = 1.5 * 2 + 1.5 * 2.5 + 2 * 2.5 + 1 / 2 * 1.5 * 2 * 2 = 14.75
Side area = 1.5 * 2 + 1.5 * 2.5 + 2 * 2.5 = 11.75

Know the radius and chord length of the arc and find the corresponding arc length

Know the radius R and chord length L of the arc, and find the corresponding arc length C?
The central angle of the arc is a
A = 2 * arc sin ((L / 2) / R) degree
=(2 * arc sin ((L / 2) / R)) * pi / 180 radians
C=R*A=R*(2*ARC SIN((L/2)/R))*PI/180

Sum: SN = 1 * 3 + 5 * 3 ^ 2 + 9 * 3 ^ 3 + +(4n-3)*3^n

Subtraction by dislocation
Sn=1*3+5*3^2+9*3^3+.+(4n-3)*3^n ,
3Sn=1*3^2+5*3^3+.+(4n-7)*3^n+(4n-3)*3^(n+1) ,
If you subtract the two expressions, you get
2Sn=-1*3-4(3^2+3^3+.+3^n)+(4n-3)*3^(n+1)
=-3-4*3^2*[1-3^(n-1)]/(1-3)+(4n-3)*3^(n+1)
=-3+18-2*3^(n+1)+(4n-3)*3^(n+1)
=15+(4n-5)*3^(n+1) ,
So Sn = [15 + (4n-5) * 3 ^ (n + 1)] / 2

What are the functions of dash and ellipsis?

Ellipsis (...) It is also called abridgement sign, which is used to omit the original text. "The omission of quotation is indicated with an ellipsis." "the omission of enumeration is indicated with an ellipsis." "speaking intermittently, it can be indicated with an ellipsis." "it is used to indicate saving the original text, incomplete sentence, incomplete meaning, etc."