(- 2a-4b) square = to be calculated using the complete square formula,

(- 2a-4b) square = to be calculated using the complete square formula,

Why does (- 2a-4b) & sup2; become (2a + 4b) & sup2;, the numbers in brackets originally have '-'? Why is there no "-" in the back?

Using the complete square formula to calculate the square of (a + b) and (- a-b), what can you find? Can you explain why?

(a+b)²=a²+2ab+b²
(-a-b)²=a²+2ab+b²
It is found that the two formulas are the same
In a square, negative numbers are squared off

If the solutions of equation 2x-6 = 0 and equation 2-5x = 2m-x are the same, then the value of M is

2X-6=0
2X=6
X=3
2-5X3=2m-3
-13=2m-3
-10=2m
m=-5

The distance between a and B is 350km. An express train and a local train leave from the two places at the same time. They meet after 3.5 hours. It is known that the speed ratio of the express train and the local train is 3:2. What are the speeds of the two trains?

350 △ 3.5 × 33 + 2, = 100 × 35, = 60 (km); 350 △ 3.5 × 23 + 2, = 100 × 25, = 40 (km); a: the speed of car a is 60 km / h, and that of car B is 40 km / h

Denominator is a fraction of 10, decimal is () decimal, denominator is a fraction of 100, decimal is () decimal

1. A decimal is (1) decimal
2. (2) is a decimal

A and B depart from a and B at the same time. A travels one tenth of the whole journey per hour, B travels 80 kilometers per hour, and when a is 260 kilometers away from a,
Car B is 320km away from ground B. find the distance between two places
Try to use arithmetic instead of equations.

B travels 80 kilometers per hour, B is 320 kilometers away from B, B travels 320 △ 80 = 4 hours
The speed of a is 260 △ 4 = 65 km / h
The distance between the two places is 65 × 10 = 650 km

The equivalence of the fundamental theorem of the completeness of real numbers
[1. The principle of supremum, 2. Monotone boundedness theorem, 3. Interval nest theorem, 4. Finite cover theorem, 5. Compactness theorem, 6. Cauchy convergence criterion] proof of mutual derivation among these six theorems (30 proofs in total)
The compactness theorem means that a bounded real number sequence must have a convergent subsequence with a real number as the limit. There is a detailed introduction to the theorem in Calculus (2) published by the higher education press, and there have been more than ten derivations and proofs,

It's very strange why LZ came here to ask, because it can be read completely, and it doesn't need 30 proofs to prove equivalence, just need to have
1=>2
2=>3
3=>4
4=>5
5=>6
6=>1
Six proofs can prove that they are equivalent

It is known that car a travels 120 kilometers per hour, 20% faster than car B. what is the distance between the two cities?
Seek the method, solution idea! Thank you!

The idea of disintegration is as follows
First of all, we know that car a is 120km / h and 20% faster than car B. then car B's speed = x x + (x x 20%) = 120
It is easy to get that the speed of car B is 100km / h
In other words, the distance between the two cities is just equal to the sum of the 1-hour walking distance of the two cars
Then the distance between the two cities is 120 + 100 = 220km
The calculation method is as follows: the speed of vehicle a is x1h + the speed of vehicle B is x1h = (120km / hx1h) + (100km / hx1h) = 220km
It is simplified as (speed a + speed b) X1 = (120km / H + 100km / h) x1h = 220km

If the average of the first four numbers is 7 and the average of the last four numbers is 10, find the average of the first number and the fifth number

The last number is: 9 × 5-7 × 4 = 17
The first number is 9 × 5-10 × 4 = 5
The average of the first number and the fifth number is: (17 + 5) △ 2 = 11

There is a number that is even and a multiple of 2 and 3. It is a two digit number, and a multiple of 5 after a digit is exchanged with a digit on a ten digit number

54