A particle moves in the XY plane, the motion equation is: x = 3T + 5, y = 1 / 2T ^ 2 + 3t-4, find the velocity expression of the particle, and calculate the velocity when t = 4 Y = 1 / 2 * (T ^ 2) + 3t-4, the above y formula is not accurate

A particle moves in the XY plane, the motion equation is: x = 3T + 5, y = 1 / 2T ^ 2 + 3t-4, find the velocity expression of the particle, and calculate the velocity when t = 4 Y = 1 / 2 * (T ^ 2) + 3t-4, the above y formula is not accurate

The derivative of X to t x '= 3, (the component of velocity along the x-axis)
The derivative of y to t y '= t + 3, (the component of velocity along Y-axis)
When t = 4, X '= 3, y' = 7
The speed is (root 58)

When a particle moves in the plane, the equations of motion are x = 2T and y = 19-2t ^ 2. What is the instantaneous velocity at the end of the second second second?

x. Y is the derivative of T, VX = 2, vy = - 4T = - 8, v = (2 ^ 2 + 8 ^ 2) ^ 0.5

The rotation speed of fan blade is 1800 / min, and the period, frequency and angular velocity are calculated

Period T = 60 / 1800 = 1 / 30 (SEC)
Frequency f = 1 / T = 30 (Hz)
Angular velocity ω = 2 π f = 60 π (rad / s)

If the side view of a cone is semicircle, then the apex angle of the cone (the angle between two generatrix in the section of the cone axis) is ()
A. 30°B. 45°C. 60°D. 90°

Let the generatrix length of the cone be r, then the circumference of the bottom surface of the cone is π R, then the diameter of the bottom surface of the cone is r, so the apex angle of the cone is 60 degrees

2.4.7 what are the last two

1+1=2
2+2=4
4+3=7
7+4=11
So it's 11

Cut the disc with circumference of 18.84cm into two semicircles of the same size. The circumference of each semicircle is______ cm．

18.84 △ 3.14 + 18.84 △ 2, = 6 + 9.42, = 15.42 (CM); answer: the circumference of each semicircle is 15.42 cm

How to calculate the side area of a triangular prism?
We need formulas. We need formulas~

Bottom perimeter × height

What is the formula of sin90 degree + cos180 degree - tan0 degree + sin270 degree

You don't have to write it out
Draw a rectangular coordinate system, according to y = sin α, x = cos α

Sum Sn = 1-5 + 9-13 + 17-21 + +(-1)^n+1(4n-3)

Because 5-1 = 4,13-9 = 4,17-13 = 4
When n = even,
sn=4*n/2=2n；
When n = odd,
sn=2(n-1)+(-1)^n*1(4n-3)

The function of dash and ellipsis
Dash:
1. From a very high hillside——
2. Go suddenly——
3. Ding Dong Ding Dong——
ellipsis:
one
2. Into my eyes, into my heart
3. Ding Dong Ding Dong

In addition to ellipsis, the ellipsis has the following uses: 1. To express silence: for example: Aunt Mei's body can no longer stand the bumps on the road 2. Language interruption: e.g. wearing a robe