Decomposition factor: A & # 179; (X-Y) - 3A & # 178; B (Y-X) =

Decomposition factor: A & # 179; (X-Y) - 3A & # 178; B (Y-X) =

a³(x－y)－3a²b(y－x)＝a³(x－y)+3a²b(x－y)
=(a³+3a²b)(x－y)
=a²(a+3b)(x-y)

Decomposition factor: - X & # 178; a-3ax-2a

-x²a-3ax-2a
=-a(x²+3x+2)
=-a(x²+x+2x+2)
=-a[x(x+1)+2(x+1)]
=-a(x+1)(x+2)

In December, the store sold the color TV at a 10% discount. On New Year's day, on the basis of a 10% discount, the store still made a profit of 7.5%. If the price of the color TV is 2000 yuan, how much is the price of the color TV

The price of color TV is 2500 yuan, and the calculation formula is: price * 90% - 100 = 2000 (1 + 7.5%)

Approximate 78 123 445 keep two significant numbers
The approximate number 7 995 123 retains three significant numbers
Approximate 0.001 237 keep three significant numbers
5 631 274 accurate to thousands

Is 7.8 × 10 to the 7th power

Happy summer vacation in 2011

1. Square of (A-2) 2.11a-33. M + n 2m + 4n4.9 + (x-3) × 2.45.16.0.57. X = 5, y = 10 plus or minus 8. Countless 39.3 - 310. △ = 7 0 = 311. X + y = - 1 2x + y = 012. X = 2, y = 513.55 21. - 22.23.204. Two thirds 5. - 26.2.257.x3 y-38.x5 Y30 three choice questions bddca

In the isosceles trapezoid ABCD, AB / / CD, e, f are two points on the edge AB, and AE = BF, de and CF are compared with each point in the trapezoid ABCD
1. Verify OE = of
On the second and third floors,
If you don't, cut in

∵ isosceles trapezoid
∴AD=BC ∠A=∠B
∵AE=BF
∴△ADE≌△BCF
∴∠AED=∠BFC
The ∧ FeO is an isosceles triangle
∴OE=OF

100-99+98-...+12-11+10

100-99+98-...+12-11+10 =(100-99)+(98-97)...+(12-11)+10=(1*45)+10=55

I'm a freshman in junior high school. I can study history, but I don't know why. After class, I forget half of the things in class, and I'll have an exam in a few days. So I'm asking questions here. I hope you can help me. First of all, I'm completely confused about feudalism, hereditary system, slavery and abdication, Please write down the key points of the first volume of Chinese history (Grade 7) for me, or write down the most common questions in previous years' examinations. If you can't, please help me sort out the development order (especially the important events and years), such as the battle of Julu and the battle of Chengpu. I will be very grateful

First
Enfeoffment system:
Enfeoffment system is also known as enfeoffment system or feudalism, which means "Feudalism" in a narrow sense. It belongs to the category of political system. The ancient patriarchal system is the basis of enfeoffment system. It is the patriarchal system in the family scope and the enfeoffment system in the country scope. The system of enfeoffment of princes by emperors in ancient China, The princes were hereditary and had the right to rule in their country, but they had the obligation to pay tribute to the emperor regularly and to provide military taxes and military service
Hereditary system:
"Hereditary system" means that after the ancient monarch stepped down, he transferred the 95% honor to his son. Hereditary system means that the name, title and property are passed down from generation to generation according to the blood relationship. This kind of inheritance mainly includes the inheritance of "parents" and the inheritance of vassal states. The inheritance of "parents" can also be divided into paternal and matrilineal. The ruling monarch also has the inheritance, and there may be blood relationship between the monarch and the monarch, But it is not necessarily the lineage. Some are brothers, some are uncles, some are nephews; some are appointed by the king; some are class grabbing, power usurping, so it is not hereditary
Slavery:
Slavery refers to the system in which slave owners own slaves. Labor activities must be dominated by slaves, without payment, and without personal freedom. Slaves generally come from prisoners of war, indigenous people in occupied areas, debtors and criminals. Slaves in recent and modern times were mostly abducted and sold to European colonies from Africa and other places. Slavery generally appeared in agricultural society. The most typical slavery in ancient times was the Roman Empire, Ancient Greece, ancient Egypt, ancient Babylon, China before the Warring States, the south of the United States before the civil war, and some colonies of Britain, France, and Russia all belonged to slavery. However, there are still disputes about whether the slave society is the necessary stage for any region and any nation
Abdication system:
In the form of abdication, the incumbent monarch voluntarily elects a successor to let a more virtuous person rule the country. Usually, abdication is to give power to a different surname, which will lead to the change of Dynasty, which is called "outer Chan"; while abdication to his blood relatives with the same surname is called "inner Chan", The abdicator is usually called "supreme emperor", which does not lead to the change of dynasty
Second:
Which version?
The battle of Julu and the battle of Chengpu will not be examined
Test site table:
Primitive people, Yuanmou people, peak cave people, Hemudu, Banpo, Yanhuang
Five emperors, the founding time of Xia (2070 BC), the founder (Yu, Qi), Shang and Zhou (Tongxia)
Five tyrants in the spring and Autumn period, seven heroes in the Warring States period, a hundred schools of thought and Shang Yang's reform
The significance of Qin Dynasty
The great events of Han Dynasty
Wei, Jin and Six Dynasties
Appendix:
Unit 1 the origin of Chinese civilization
Lesson 1 ancient inhabitants of the motherland
Lesson 2 primitive farming life
Lesson 3 the ancestor of China
Unit 2 the emergence of the state and social change
The rise and fall of Xia, Shang and Western Zhou
Lesson 5 splendid bronze civilization
Disputes in the spring and Autumn period and the Warring States Period
Lesson 7 the era of great change
The rise of Chinese culture (1)
The rise of Chinese culture (2)
Unit 3 the establishment of a unified country
Lesson 10 "the king of Qin sweeps Six Harmonies"
Lesson 11 "cutting down the lawless and killing the violent Qin"
Lesson 12 the unified Han Dynasty
Economic development in the Han Dynasty
The rise of Xiongnu and the war with Han Dynasty
Lesson 15 han to the western regions and the Silk Road
Prosperous culture of Qin and Han Dynasties (1)
Prosperous culture of Qin and Han Dynasties (2)
Unit 4 separation of political power and national integration
Lesson 18 Three Kingdoms
Lesson 19 development of Jiangnan region
Lesson 20 northern ethnic integration
The culture of Wei, Jin, southern and Northern Dynasties
The culture of Wei, Jin, southern and Northern Dynasties (2)
Check the book by yourself!

In the isosceles triangle ABCD, ad is parallel to BC, point E is a point on the extension line of AD, de = BC. 1. Prove: angle f = angle DBC. 2. Try to find the shape of ace
In the isosceles trapezoid ABCD, ad is parallel to BC, point E is a point on the ad extension line, de = BC. 1. Verification: angle f = angle DBC 2. Try to find the shape of triangle ace.

1. Because e is a point on the extension line of AD, De is parallel to BC, and because de = BC, quadrilateral DECB is parallelogram, so angle e = angle DBC
2. In the isosceles trapezoid ABCD, AC = BD, because the quadrilateral DECB is parallelogram, so BD = CE, that is AC = CE, so the triangle ace is isosceles triangle

1／2×3+1/3*4+1/4*5+.+1/19*20＝?

The answer is 9 / 20
The principle is 1 / [n * (n + 1)] = 1 / n-1 / (n + 1)
So the original formula = 1 / 2-1 / 3 + 1 / 3-1 / 4 +... + 1 / 19-1 / 20
=1/2-1/20
=9/20