Calculation: 1 - [a - (1 / 1-A)] ^ 2 △ (a ^ 2-A + 1 / A ^ 2-2a + 1)

Calculation: 1 - [a - (1 / 1-A)] ^ 2 △ (a ^ 2-A + 1 / A ^ 2-2a + 1)

Calculation: (a + 2) (A-2) (a ^ + 2A + 4) (a ^ - 2A + 4) (a-b) (a + b) (- A + b) (- a-b)

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

It can be found that when the numbers in brackets are all opposite, that is, the square of the whole formula multiplied by minus 1 is equal to the original formula

A unit carries out tree planting activities. If only one person plants trees, it will take 80 hours to complete. Now some people plant trees for 5 hours first. Due to the emergency of the unit, another 2 people will be added
As a result, it took another four hours to complete the task. If the efficiency of these people is the same, how many people have been arranged to plant trees in the first five hours (equation)

1 / 80 * 5x + (x + 2) * 1 / 80 * 4 = 1, the solution is x = 8, that is, 8 people are arranged

If y = the absolute value of X + 1 and - 2 ≤ x ≤ 2, find the minimum and maximum of Y

-2 ≤ x ≤ 2
-1 ≤ x + 1 ≤ 3
So 0 ≤| x + 1 | ≤ 3
therefore
The minimum value of Y is 0
The maximum value of Y is 3

There are 55 students in class 6 (1), and at least () students have their birthdays in the same month
Urgent! There's another way. How can we make it simple?

【1】
55/12=4.7
4 + 1 = 5 people
There are 55 students in class 6 (1), and at least [5] of them have their birthdays in the same month
Note:
At least number = quotient + 1
Can divide up to a few = quotient
【2】
7/15×3/8+1/15×7/16+1/15×7/2
=7/15（3/8+1/16+1/2）
=7/15（6/16+1/16+8/16）
=7/15×15/16
=7/16
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Simplification: 1 + (quadratic of a-quadratic of B / quadratic of a-Ab) △ 1 / A

1 + (quadratic of a-quadratic of B / quadratic of a-Ab) △ 1 / A
=1+（a+b）（a-b）/a(a-b)xa
=1+a+b
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The distance between the two places is 360 km. The passenger cars and freight cars leave each other at the same time and meet each other four hours later. It is known that the speed of the passenger cars is 80% of that of the passenger cars. How many kilometers do the freight cars travel per hour?

The speed of a given bus is 80% of that of a bus. It should be 80% of that of a given truck
360 ／ 4 ／ (1 + 80%) = 50 km / h
50 × 80% = 40 km / h
The truck travels 40 kilometers per hour

It is known that the equation (ab-2b) x & sup2; + 2 (B-A) x + 2A AB = 0 has two equal real roots, then the value of 1 / A + 1 / B is

It can be seen from the meaning of the title: 4 (B-A) & sup2; - 4 (ab-2b) (2a-ab) = 0
（A＋B）²－2AB（A＋B）＋A²B²＝0
（A＋B－AB）²＝0
∴ A＋B－AB＝0
A＋B＝AB
∴1/A＋1/B＝（A＋B）/AB＝AB/AB＝1

Car a travels 50 kilometers per hour and car B 40 kilometers per hour. Now, car a and car B start from a and B at the same time, facing each other for 4 hours
Car a travels 50 kilometers per hour, while car B travels 40 kilometers per hour. Now car a and car B start from a and B at the same time, face each other, and meet each other in 4 hours. If car a and car B go from a and B in the same direction, how many hours can car a catch up with car B? (good reward)

(40 + 50) times 4 = 360360 divided by (50-40) = 36 (hours)