The image of the function y = - xcosx,

The image of the function y = - xcosx,

How many grams of oxygen is there in a cubic meter of air

The normal air composition calculated by volume fraction is: nitrogen (N2) accounts for about 78%, oxygen (O2) accounts for about 21%
So the volume of oxygen in 1m ^ 3 air is about 0.21m ^ 3, that is 210L
Under the standard condition, the mass of oxygen is:
[210L / (22.4L/mol)] * 32g/mol = 300g

If for any non-zero rational numbers a and B, the definition operation is as follows: a ⁃ B = B / A-2, then what is the value of (- 6) ⁃ 2? (- 6) ⁃ 2 ⁃ 1

One by one into the not out?
（-6）※2 = 2/(-6-2) = -1/4
(-6）※2※1 = (-1/4)※1 = 1/(-1/4-2) = 1/(-9/4)=-4/9

Calculation formula of volume and surface area of sphere

The calculation formula of sphere surface area is s = 4 π R & # 178;
The calculation formula of sphere volume is: v = (4 / 3) π R & # 179;
Hope to adopt!

In fact, Vega is 26 light-years away from the earth, Altair is 17 light-years away from the earth, can you calculate
In fact, Vega is 26 light-years away from the earth, and Altair is 17 light-years away from the earth. Can you calculate how many kilometers Altair and Vega are away from the earth? If they are really close to each other at the speed of light, can you guess whether they are possible
Meet once a year?
List the formulas and write them

The first problem cannot be calculated because of the lack of angle data of Samsung connection
According to the data, Niulang and Zhinv are separated by 16.4 light years
If they are close to each other at the speed of light, it will take 8.2 years

In the 5th century BC, Zu Chongzhi, an ancient mathematician of our country, calculated that the approximate value of PI was between 3.1415926 and 3.7415927. If four significant numbers were retained, the approximate value of PI would be, accurate to

3.142
Accurate to the thousandth

Let d be a plane region bounded by a curve y = √ (2x-x ^ 2) and a straight line x + y = 2, and find I = ∫ ∫ (D is an integral region) (x + y) DXDY

First, we find out the intersection point: {y = √ (2x - X & # 178;) {y = 2 - x to get (1,1), (2,0) I = ∫ ∫ (x + y) DXDY, polar coordinates = ∫ (1 → 2) ∫ (2 - x → √ (2x - X & # 178;)) (x + y) dydx = ∫ (1 → 2) (XY + Y & ∫ / 2): (2 - x → √ (2x - X & # 1)

The perimeter of a rectangle is 38 cm. It is known that its length and width are two prime numbers. What is the area of the rectangle?

Add length and width = 19
19 is an odd number, equal to the sum of an odd number and an even number
Even prime is 2,19-2 = 17
Area 2 * 17 = 34

The detailed steps of solving limx → 0 (1 / X-1 / e ^ x-1) with lobita rule

General division
=lim(e^x-1-x)/x(e^x-1)
=lim(e^x-1)/(e^x-1+x*e^x)
Or 0 / 0
=lim(e^x)/(e^x+e^x+x*e^x)
=lim1/(2+x)
=1/2

The equation X225 − m + y2m + 9 = 1 represents an ellipse with focus on the y-axis, then the value range of M is______ ．

∵ the equation X225 − m + y2m + 9 = 1 represents the ellipse with the focus on the Y axis, ∵ m + 9 > 25-m > 0, ∵ 8 < m < 25