Simple calculation of 9.6 plus 9.9 times 99 4.65 times 32 plus 2.5 times 46.5 plus 0.465 times 430

Simple calculation of 9.6 plus 9.9 times 99 4.65 times 32 plus 2.5 times 46.5 plus 0.465 times 430

=9.6+9.9x99 =4.65x32+2.5x46.5+0.465x430
=9.6+(9.9x100)-9.9 =46.5x3.2+46.5x2.5+46.5x4.3
=9.6+990-9.9 =46.5x(3.2+2.5+4.3)
=989.3 =46.5x10
=465

It takes 30 seconds for a train to pass through a 1200m long tunnel. Given that the length of the train is 150m, what is the speed of the train?

(1200 + 150) / 30 = 45 m / S

As shown in the figure, points a, B, C, D are on the circle O, ab = AC, ad and BC intersect at point E, AE = ed / 2, extend DB to point F, make FB = BD / 2, connect AF
Prove △ Abe ∽ ADB; prove that the line AF is tangent to the circle o

1、∵AB=AC
∴∠ABC=∠ACB
∵∠ ACB = ∠ BDA (equal to the circle angle on the same arc)
∴∠ABC=∠BDA
That is, Abe = BDA
∵∠BAE=∠BAD
∴△ABE∽△ADB
2. ∵ AE = ed / 2, i.e. AE / ed = 1 / 2
FB = BD / 2, that is FB / BD = 1 / 2
∴AE/ED=FB/BD
∴(AE+ED)/ED=(FB+BD)/BD
That is ad / ed = BD / DF
∵∠ADF=∠EDB
∴△ADF∽△EDB
∴∠EBD=∠AFD
∴AF∥BE
∴∠FAB=∠ABE=∠BDA
That is, Fab = FDA
∵∠AFB=∠AFD
∴△AFB∽△ADF
∴AF/DF=BF/AF
That is AF & # 178; = BF × DF
The tangent of line AF and circle O (the inverse theorem of cutting line)

Why is the speed of electric field equal to the speed of light?
Such as the title

When the electric field changes, it propagates in the form of electromagnetic wave. The speed of electromagnetic wave in vacuum is the speed of light
The speed of the electron can be very close to the speed of light, but it can never reach the speed of light. Because the electron is a physical particle with mass, according to the relativity theory, when the speed of the physical particle with mass reaches the speed of light, the mass will become infinite, so it is impossible for the electron to reach the speed of light
When the electromagnetic field has no change, it is meaningless to talk about the propagation speed, or think that its speed can be arbitrarily large (of course, it can exceed the speed of light). When the electromagnetic field has a change, it will spread in the form of electromagnetic wave, and the propagation speed is the speed of light, so the electromagnetic field is not light, the change of electromagnetic field produces electromagnetic wave, and the second light is a kind of electromagnetic wave

China Mobile introduces two mobile phone billing methods: (1) monthly rent 18 yuan, call fee 0.2 yuan / minute; (2) monthly rent 0 yuan, call fee
40 yuan / min. (1) when the call time is 100 minutes in a month, the charges of the two methods are the same? (2) if the call time is 100 minutes in a month, which method is more economical? (3) if the call fee is fixed at 50 yuan, which method is more economical?

Set the call time as X, and the unit is minutes
(1) the first charging standard is 18 + 0.2x
The second charging standard is 0.4x
When the two kinds of charges are equal, that is, 18 + 0.2x = 0.4x, the solution is x = 90
So when a month's talk time is 90 minutes, the two kinds of charges are the same
(2) when the monthly call time is 100 minutes, according to the first tariff, the required call fee is 18 + 0.2 × 100 = 38 yuan
According to the second tariff, the required call fee is 0.4 × 100 = 40 yuan, obviously 38 < 40 yuan
Therefore, the cost of choosing the first one is low, and the first tariff standard should be chosen
(3) if the charge is fixed at 50 yuan, the first charge is 18 + 0.2x = 50, then x = 160
If the second tariff is 0.4x = 50, then x = 125, obviously 160 > 125
So it's cost-effective to choose the first one

As shown in the figure: in square ABCD, the crossing point D is DP, AC is crossed at point m, AB is crossed at point n, and the extension line of CB is crossed at point P. if Mn = 1, PN = 3, the length of DM is______ ．

Let DM = x, Pb = y, and the side length of square ABCD be Z, then DN = x + 1 ∵ ad ∥ PC ∥ ADM ∥ CPM, △ PNB ∥ DNA ∥ pndn = PBAD ∥ 3x + 1 = YZ, 4x = y + ZZ = YZ + 1, 3x + 1 = 4x-1, 3x = 4 (x + 1) - x2-x, x = 2 or - 2 (rounding off), ∥ x = 2

According to the density formula, the mass of 22.5 cubic decimeters of pure water is () kg, and 150000 grams of pure water accounts for () m3

I'm glad to answer your question
The density of pure water is 1kg / DM ^ 3
m=pv=1kg/dm^3×22.5dm^3
=22.5kg
150000g=150kg
v=m/p=150kg/1kg/dm^3
=150dm^3

During the summer vacation, Li Li took a bus to her grandmother's home, leaving at 9:30 a.m. and arriving at 3:30 P

3:30 PM = 15:30 PM
65 * (15:30-9:30) = 65 * 6 = 390km

After cutting 2.5cm along the length and width of a rectangle, the area is 28 square centimeters less than the original. What is the perimeter of the original rectangle?

Let the length be x and the width be y
Then (x-2.5) (y-2.5) = xy-28
xy-2.5y-2.5x+6.25=xy-28
2.5(x+y)-6.25=28
2(x+y)=27.4
The perimeter of the original rectangle is 27.4cm
For reference only

In known triangle ABC, angle c = 120 degrees, C = 7, a + B = 8 (a)

Cosine theorem:
a^2+b^2-2abcosC = c^2
a^2+b^2+ab = 49
And a + B = 8
a