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1949+1950+1951+…… +2010/1950+1951+1952+…… +2010 (1949+1950+1951+…… +2010)/(1950+1951+1952+…… +2010).
1949+1950+1951+…… +2010=（1949+2010）*62/2
1950+1951+1952+…… +2010=（1950+2010）*61/2
（1949+2010）*62/2/（1950+2010）*61/2
=3959*62/3960*61
=122729/120780
(1949+1950+1951+…… +2010)/(1950+1951+1952+…… +2011).
=3959/3961
The above formula = (1949 + 2010) * 62 / 2
The following formula = (1950 + 2011) * 62 / 2
Up / down = (1949 + 2010) / (1950 + 2011) = 3959 / 3961
In a right triangle, AC = 60, CB = 80, angle c = 90 ° point P moves from point C to Ca edge at a speed of 3cm per second, while another point Q moves from point C along CB edge to point B at a speed of 4cm per second. After a few seconds, the distance between two points is 40
Let time be t, CP = 3T, CQ = 4T
If be: BC = 3:7, then EF: EA=____
A: I don't have a picture to fill in
Because: the opposite sides of parallelogram are parallel and equal
So: AD / / BC, ad = BC
So: △ EBF ∽ ADF
So: be / DA = EF / AF
So: be / BC = EF / AF = 3 / 7
So:
EF/(AF+EF)=3/(3+7)
So: EF / EA = 3 / 10
A man-made earth satellite with a mass of m moving in a circular orbit. Its distance to the earth is equal to the radius r of the earth, the distance on the ground
The velocity of satellite a is root 2rg
The acceleration of B satellite is p root P / Q
The period of C satellite motion is 4 π radical 2R / g
The kinetic energy of D satellite is 1 / 4 MRG
The satellite moves in a circle, and gravity provides the centripetal force, GMM / 4R ^ 2 = MV ^ 2 / 2R. (1) on the ground, there is: Mg = GMM / R ^ 2. (2) get: v = root sign, Gr / 2 a wrong, GMM / 4R ^ 2 = ma. (3) get: a = g / 4 B don't know what to write, GMM / 4R ^ 2 = M4 π ^ 2 * 2R / T ^ 2. (4) get: T = 4 π root sign, 2
All formulas of cylinder and cone, such as height, side area, bottom area, bottom perimeter, surface area, etc., should be pure, not π and so on
You can do those pions and stuff like that, but you have to put those things on, and so on
Cylinder side area = bottom area * height = square of bottom radius * 3.14 * height
Bottom area of cylinder = square of bottom radius * 3.14
Circumference of cylinder bottom = bottom radius * 2 * 3.14
Surface area of cylinder = side area + bottom area * 2 = square of bottom radius * 3.14 * height + square of bottom radius * 3.14 * 2
Cylinder volume = base area * height
Side area of cone = square of generatrix length * 3.14 * (degree of central angle of sector after side expansion / 360)
Surface area of cone = side area + bottom area
Cone volume = 1 / 3 * bottom area * height
The perimeter of a rectangle is 130 cm. If the length is increased by 2 / 7 and the width is decreased by 1 / 3, the perimeter of the new rectangle is equal to that of the original rectangle, and the area of the original rectangle is calculated
2X+2Y=130
9/7X+2/3Y=65
X=35 Y=30
Area = 1050
Take the approximate value according to the rounding method, and fill in "()" when replying
Keep integer: keep one decimal place: keep two decimal places: keep three decimal places:
153.8 （ ） （ ） （ ） （ ）
76.172 （ ） （ ） （ ） （ ）
88.4/45（ ） （ ） （ ） （ ）
53.77/33 （ ） （ ） （ ） （ ）
Keep integer: keep one decimal place: keep two decimal places: keep three decimal places:
153.8 （ 154 ） （ 153.8 ） （ 153.80 ） （153.800 ）
76.172 （ 76 ） （ 76.2 ） （ 76.17 ） （76.172 ）
88.4/45（ 2 ） （ 2.0 ） （ 1.96 ） （1.964 ）
53.77/33 （ 2 ） （ 1.6 ） （ 1.63 ） （ 1.629 ）
It takes 80 seconds for a train to pass a 456 meter long bridge, and 77 seconds to pass a 399 meter long tunnel at the same speed
Set the train length L and the speed v
According to the meaning of the title:
(399+L)/V=77
(456+L)/V=80
The solution is L = 1064m, v = 19m / s
The length and width of a rectangle have been increased by 5cm and the area has been increased by 125cm2. What is the original perimeter of this rectangle
It is better to have only one unknown
Liu Longmo,
Analysis: length is a, width is B, length increases by 5cm, area increases by 5b, width increases by 5cm, area increases by 5a, at the same time, there is also a square with side length of 5cm
The original sum of length and width is:
(125-5 × 5) △ 5 = 20 (CM)
Original rectangle perimeter:
20 × 2 = 40 (CM)
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