The square of a + (a + 1) (A-1) - 2A (a + 1)

The square of a + (a + 1) (A-1) - 2A (a + 1)

a^2+（a+1)(a-1)-2a(a+1)
=a^2+a^2-1-2a^2-2a
=-2a-1

The square of a-2a = 1
What is a

The square of a - 2A = 1;
a²-2a+1=1+1;
(a-1)²=2;
a-1=±√2;
a=1±√2;
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If we know that the shape of the parabola y = ax ^ 2 + C is the same as that of y = - 3x ^ 2, and the opening is downward and passes through the point (2,9), then the expression of the parabola is_____________

It is known that the shape of the parabola y = ax ^ 2 + C is the same as that of y = - 3x ^ 2, and the opening is downward,
The expression of the parabola is: y = - 3x & # 178; + 21

One by half plus two by one-third plus three by one-quarter Plus 49 times 50=

If the value of fraction x ^ 2 + 2x-3 / X-1 is O, then x =?
The value of x ^ 2 + 2x-3 / X-1 is 0

x=-3.

2Y + 4Y = 15, solve the equation

6y=15
y=15÷6
y=2.5

To solve the equation: 5x-2 = - 7x + 10 6 / 5Y + 4 / 1 = 1-6 / 1y

5x-2=-7x+10
Both sides + 7x + 2
12x=12
x=1
5Y of 6 + 1 of 4 = 1y of 1-6y
Multiply both sides by 12
10y+3=12-2y
Both sides + 2y-3
12y=9
y=3/4

On the application of solutions to linear equations of one variable
3. A Xinhua bookstore has several original books. One half of them were sold in the first day. The next day, 900 books were brought in. On the third day, 40 more than one third of the existing books were sold. As a result, there are still 800 books in the bookstore. How many original books are there in the bookstore
4. A barrel of oil weighs 11 kg. After three fourths of the oil is put everywhere, the remaining oil and the barrel are 3.5 kg in total. How many kg does the barrel weigh and how many kg does the barrel weigh
5. If the sum of the degrees of the two angles is 146 ° and their difference is 82 °, calculate the degrees of the two angles
6. The school has purchased a number of computers. If 40 computers are installed in each computer classroom, there are still 15 missing. If 35 computers are installed in each computer classroom, there are 20 more. Q: how many computers have the school purchased? How many computer classrooms does the school have? Please design a plan for the school to install all the purchased computers
7. A rectangular vegetable field, 40 meters long and 35 meters wide, is planted with cucumbers and tomatoes. If the area of cucumbers is 80% larger than that of tomatoes, how many square meters of cucumbers and tomatoes are planted?

1. Set the original x book
(X/2+900)-1/3*(X/2+900)-40=800
X = 720 copies
2. If you set up an oil tank of x kg, you have X-11 kg
(1-3/4)X+X-11=3.5
X = 11.6kg barrel has 11.6-11 = 0.6kg
3. Let these two angles be x and y
X+Y=146
X-Y=82
The solution is x = 114, y = 32
4. There are x classrooms
Then 40x-15 = 35x + 20
X = 7 computers have 40 * 7-15 = 265 computers
The scheme sells 265 + 15 = 280 computers or 265-20 = 235 computers
5. The area of vegetable field is 40 * 35 = 1400
If x square meters of tomatoes are planted, there will be (1 + 80%) x square meters of cucumbers
X+（1+80%）X=1400
X = 500 square meters
That is 500 square meters of tomatoes, cucumber 1400-500 = 900 square meters

A necessary and sufficient condition for n-order real symmetric matrix A to be positive definite
A. A ^ - 1 is a positive definite matrix
All k-order subformulas of B a are greater than zero
The rank of C A is n

Choose A. let a ^ - 1's eigenvalues be A1, A2,... An. Then the eigenvalues of a are 1 / A1, 1 / A2,. 1 / an. Because all an are greater than 0, all 1 / an are greater than 0. So choose A. in addition, if B item is changed to a11 > 0 and the first determinant of determinant of each order (you can't make a formula, you can only use words to express

This is a factorization problem X & # 178; + 2XY + Y & # 178; = () 25X & # 178; + 10x + 1 = ()

x²+2xy+y²=(x+y )² 25x²+10x+1=（5x+1 ）²
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