It is proved that the function y = x + 2x is a decreasing function in (- ∞, - 1)

It is proved that the function y = x + 2x is a decreasing function in (- ∞, - 1)

According to the definition field (- infinity, - 1), let x1 ＜ x2 ＜ - 1F (x2) - f (x1) = (x2 & # 178; + 2x2) - (x1 & # 178; + 2x1) = (x2 & # 178; - X1 & # 178;) + (2x2-2x1) = (x2 + x1) (x2-x1) + 2 (x2-x1) = (x2-x1) (x2 + X1 + 2) ∧ x1 ＜ - 1 ∧ 0, (x2 + x1) ∧

Verification: y = (2x + 3) / (x-1) is a decreasing function when x > 1

It's unnecessary to verify. Just replace a few numbers > 1 to see if the larger x is, the smaller y is
Certificate:
Let 11 x2-1 > 0 x1-1 > 0
x2>x1 x2-x1>0
-5

It is proved that the function y = x + 2 / x + 1 is a monotone decreasing function on (- 1, positive infinity)

Let x1, X2 be on (- 1, positive infinity), and x1

China's arable land area accounts for one ninth of the national territory!

China's arable land area accounts for one ninth of the national territory. (territorial area) × one ninth = (arable land area)

If we calculate the electrostatic force between point charges, we can use Coulomb's law, right

Right
The concept of point charge is similar to that of particle
The derivation of kuhua theorem is based on the condition of point charge in vacuum. In general, as long as the sphere or object with a point in the atmosphere does not affect the distance between the centers of two spheres or objects, it can be regarded as the formula of point charge, and it can also be calculated by kuhua formula
However, we should pay attention to one point here, that is, the redistribution of charges. When two spheres meet and then separate, the same kind of charges are evenly distributed, and the different kinds of charges are first offset and then evenly distributed

August 8, 2010 is Sunday. What day is the 100th day after that

Tuesday
100/7=14…… two
Then, 14 weeks have passed since Sunday, and the remaining two days are Tuesdays

The difference between symbolic expression and chemical equation
Are symbolic expressions the same as chemical equations?
Note: it's a symbolic expression
The difference between

If the symbolic expression is not balanced, just write the reactant and the product, the middle is not needed = use → but the reaction conditions are all to be written, and the coefficients are all 1, so no balancing is needed
The chemical equation is to be balanced
I remember that when I was in junior high school, I learned expressions. In senior high school, I used equations

1 000 ^ 2 of 252 ^ 2-248 ^ 2 (factorization,

Original formula = (252 + 248) (252-248) parts of 1000 ^ 2
=1000 ^ 2 of 2000
=500

A mathematical problem of permutation and combination probability,
Randomly selected nine students, at least two students were born in the same month, the probability is?

At least two students were born in the same month, and the opposite is that all students were not born in the same month,
C (m, n) where m is the upper coordinate and N is the lower coordinate,
C(2,9)*A(9,12)/9^12

Rational number multiplication problem minus 105 times (one third minus five seventh minus two fifths) to step!

-105*(1/3-5/7-2/5)
=-105*1/3+105*5/7+105*2/5
=-35+75+42
=82