Why does the author say "people who prefer to study at Peking University" in "the chance of 13 years old"? What are the characteristics of people in Peking University? Just today

Why does the author say "people who prefer to study at Peking University" in "the chance of 13 years old"? What are the characteristics of people in Peking University? Just today

Express the author's yearning for Peking University
People of Peking University: the sensitivity, purity, wit and vitality of the students of Peking University make the author feel the unique fresh and free atmosphere of Peking University. The teachers of Peking University make the author understand the real meaning of the word "teacher" for the first time: rigorous scholarship and sincere life

What's the role of this sentence in the structure of the article

This sentence plays a connecting role in the text, is a transitional sentence

Why does the author love Peking University so much at the age of 13
We need internal reasons
For internal reasons, it's faster than half an hour

Because she has a genetic relationship with Peking University
Peking University gave her knowledge and happiness
She spent a substantial time in Peking University

The relationship between the rank of coefficient matrix and the solution of homogeneous linear equations?

If the coefficient matrix is full rank, then the homogeneous linear equations have and only have zero solutions. If the coefficient matrix is reduced rank, then there are infinite solutions, and the number of vectors of the basic solution system is equal to n-r

Given x 2-7x + 1 = 0, find the value of x 2 + X-2

Because x2-7x + 1 = 0, so x ≠ 0, then divide both sides of the equation by X to get X-7 + X-1 = 0, that is, x + X-1 = 7, so (x + x-1) 2 = x2 + 2x. X-1 + (x-1) 2 = 49, X2 + 2 + X-2 = 49, so x2 + X-2 = 47

It is known that the absolute value of a in a + the absolute value of B in B + the absolute value of C in C = minus one. Try to find the absolute value of AB in ABC

∵|A|/A+|B|/B+|C|/C=-1
There are two negative numbers and one positive number in a, B and C
(| a | / A + | B | / B + | C | / C has four values in total
3 positive: the result is 3; 3 negative: the result is - 3;
2 positive 1 negative result is 1; 2 negative 1 positive result is - 1)
∴ABC>0
∴ABC/|ABC|=1

If the solutions X and y of the equations 2x = y + 3 2kx - (k-1) y = 6 are opposite to each other, then K=

Bring y = - x in
2x=-x+3
x=1
y=-1
2k+k-1=6
3k=7
k=7/3

In integral calculation, what is the + ∞ power of e equal to?
That is to calculate the integral of - e ^ (- 4x) in (k, + ∞), where the + ∞ power of E is equal to what?
Are there any rules here?

-∫（k,∞）exp（-4x）dx=0.25∫（k,∞）exp（-4x）d(-4x)
=0.25exp (- 4x) ∣ (k, ∞) (here the upper limit is replaced by ∞ and the lower limit by K)
Finally, we get the value of integral: = - 1 / (4exp (4K))
Here only exp (- ∞) = e ^ (- ∞) = 0, and e ^ (+ ∞) = ∞

In the triangle ABC, D is on the edge of BC, and CD vector = - 2bd vector. If CD vector = PAB vector + QAC vector, then p + q =?

CD vector = - 2bd vector
Then: CD vector = (2 / 3) CB vector = (2 / 3) (CA vector + AB vector) = (2 / 3) (AB vector AC vector)
And: CD vector = PAB vector + QAC vector
(2 / 3) (AB vector AC vector) = PAB vector + QAC vector
[(2 / 3) - P] AB vector = [(2 / 3) + q] AC vector
AB vector, AC vector, different directions
Only: (2 / 3) - P = 0, (2 / 3) + q = 0
p=2/3,q=-2/3
So: P + q = 0

On the concept of limit and derivative
Let f (x) be bounded and differentiable in (0, + ∞)
If the limit of F (x) is zero, then the limit of F (x) derivative must be equal to zero. Why is it wrong
If the limit of F (x) derivative exists, then the limit of F (x) derivative must be zero
2. If the second derivative of function f (x) exists at x = A and is less than zero, and if the derivative is equal to zero at a, then there must be Δ > 0
A curve y = f (x) is convex in the interval (a - Δ, a + Δ)
The b-curve y = f (x) increases strictly monotonically in the interval (a - Δ, a) and decreases strictly monotonically in the interval [a, a + Δ]
The B option of this question is correct, but I don't think there is much difference between a and B, please answer~~~~

If the limit of F (x) is zero, then the limit of F (x) derivative must be equal to zero. Why is it wrong? Consider the function y = (SiNx ^ 2) / x, y '= [(cosx ^ 2) 2x · x-sinx ^ 2] / x ^ 2 = 2cosx ^ 2 - [(SiNx ^ 2) / x ^ 2] LIM (x → + ∞) y = 0, but LIM (x → + ∞) y' does not exist