1. X & # 178; + xy-2y & # 178; 2. M & # 178; + 5mn-50n & # 178; 3. (x + 1) &# 178; - x (x + 2) factorization

1. X & # 178; + xy-2y & # 178; 2. M & # 178; + 5mn-50n & # 178; 3. (x + 1) &# 178; - x (x + 2) factorization

1 （x+2y）（x-y）
2 （m-5n）(m+10n)
There is no factorization. The answer is 1

Given X-Y = 1 / 2, xy = 4 / 3, find x ^ 2y-xy ^ 2 =?
Solving problems by factorization

X^2Y-XY^2
=xy(x-y)
=1/2*4/3
=2/3

Find the chord length of the line 2x + Y-3 = 0 cut by the parabola x square = - 4Y

The straight line 2x + Y-3 = 0, that is y = 3-2x, is substituted into the parabolic equation x & # 178; = - 4Y, that is X & # 178; = - 4 (3-2x) ｜ X & # 178; - 8x + 12 = 0 ｜ (X-2) (X-6) = 0 ｜ x = 2, x = 6, that is intersection a (2, - 1), B (6, - 9) ｜ chord length | ab | = √ [(2-6) &# 178; + (- 1 + 9) &# 178;] = √ 80 = 4 √ 5

A math problem: x ^ - n = 2, y ^ - n = 3; (x ^ 2Y ^ 2) ^ - n =?

Analysis
(x²y²)^-n
=x^(-2n)y^(-2n)
=(x^-n)²(y^(-n)²
=4x9
=36

How to do it by using the two side theorem?
One of N plus one of the squares of N + 1 is added to the square of (2n)
When n tends to infinity, the limit is obtained
What's the formula on the left? The one on the right?

Find: Lim [1 / N ^ 2 + 1 / (n + 1) ^ 2 +... + 1 / (2n) ^ 2] (n →∞) because: 1 / N ^ 2 + 1 / N ^ 2 +... + 1 / N ^ 2 (n 1 / N ^ 2) ≤ 1 / N ^ 2 + 1 / (n + 1) ^ 2 +... + 1 / (2n) ^ 2 ≤ 1 / N (n + 1) + 1 / (n + 1) (n + 2) + 1 / (n + 2) (n + 3) +... + 1 / (2n-1) 2n, that is: n / N ^ 2 ≤ 1 / N ^ 2 + 1 / (n + 1) ^ 2 +... + 1 /

[1]-3(-x+2y)=? [2]n-3(4-2m)=?

【1】3x-6y【2】n-12+6m

The theorem of the example of the big one and the high number
There are a lot of examples and theorems in Tongji edition. Do you have to remember them? Some examples prove a theorem, but you can't understand it,

Remember the formula can be oh! Read more on the example, deduce the formula depends on your interest Oh! Freshman or relatively simple! The teacher assigned the homework that must be done, and to understand! The exam is basically OK

Let x ~ n (- 3,1), (2,4) be random variables, and X and y are independent of each other, then x-2y + 11 ～

E(X-2Y+11)=(-3-2*2+11)=4
D(X-2Y+11)=D(X)+4D(Y)=17
N(4,17)

The problem of finding the limit of higher numbers Please explain

The molecular partition line is rational LIM (x → - 8) [√ (1-x) - 3] / (2 + cubic radical 3) = LIM (x → - 8) [√ (1-x) - 3] [√ (1-x) + 3] [4 + cubic radical x + cubic radical x ^ 2] / {(2 + cubic radical x) [√ (1-x) + 3] [4 + cubic radical x + cubic radical x ^ 2]} = LIM (x → - 8) (- X-8) [4 + cubic radical x

Given the random variables X ~ n (- 3,1), n (2,1), and X, y are independent of each other, z = x-2y + 7, then Z~
What is d (x) e (x) formula.. e (x) = NP D (x) = NP (1-p)
How about e (y) d (y)?

X-2y + 7 is normal distribution
And there are
E(X-2Y+7) = E(X)-2E(Y)+E(7) =-3 -2·2+7 =0
D(X-2Y+7) =D(X) +(-2)²D(Y) + D(7) =1+4+0=5
So n (0,5)
Formula D (x) = E [x-e (x)] ^ 2