1/((x-1)*(x-2))+1/((x-2)*(x-3))+1/((x-3)*(x-4)).+1/((x+2006)*(x-2007)) It's hard, it's hard to reach the sky! Hint: it's one of (x-1) * (X-2) plus.. it's an ellipsis. It's about the addition and subtraction of fractions

1/((x-1)*(x-2))+1/((x-2)*(x-3))+1/((x-3)*(x-4)).+1/((x+2006)*(x-2007)) It's hard, it's hard to reach the sky! Hint: it's one of (x-1) * (X-2) plus.. it's an ellipsis. It's about the addition and subtraction of fractions

1 / (x-1) (X-2) = 1 / (X-2) - 1 / (x-1) similarly, 1 / (X-2) (x-3) = 1 / (x-3) - 1 / (X-2) 1 / (x-3) (x-4) = 1 / (x-4) - 1 / (x-3). 1 / (x-2006) (x-2007) = 1 / (x-2007) - 1 / (x-2006) 1 / ((x-1) * (X-2)) + 1 / ((X-2) * (x-3)) + 1 / ((x-3) * (x-4)). + 1 / ((x + 2006) * (x-2007)) =

Simplification: X (x + 1) 1 + (x + 1) (x + 2) 1 + (x + 2) (x + 3) 1 +. + (x + 2006) (x + 2007) 1 +

1/x(x+1)=1/x-1/(x+1)
1/(x+1)(x+2)=1/(x+1)-1/(x+2)
.
1/(x+2006)(x+2007)=1/(x+2006)-1/(x+2007)
X (x + 1) 1 + (x + 1) (x + 2) 1 + (x + 2) (x + 3) 1 +. + (x + 2006) (x + 2007) 1
=1/x-1/(x+1)+1/(x+1)-1/(x+2)+.+1/(x+2006)-1/(x+2007)
=1/x-1/(x+2007)
=2007/x(x+2007)

1/(x+1)(x+2)+1/（x+2）（x+3）.1/(x+2006)(x+2007)=?

1/(x+1)(x+2)=1/(x+1)-1/(x+2)
In the future, all items will be opened in this way, right

If x is less than B and X is greater than a (a is not equal to b), then the solution set of X is less than 2-B and X is greater than 2-A?

Xa has no solution, a ≠ B
Then a > B
The solution set of x2-a is:
2-a

How much is 1 / 2 times 2 / 3 times 3 / 4, etc. times 99 / 100?

It's 1 / 100

The sequence {an}. A0 = 1, an = A0 + A1 +. An-1 (n is greater than or equal to 1), then how much an is equal to. An = A0 + A1 +... + an-1, an + 1 = A0 + A1... + an why an + 1 = 2A, why an = 2 ^ n-1

Because an = A0 + A1 +. + a (n-1)
So a (n + 1) = A0 + A1 +. + an
So a (n + 1) - an = an
So a (n + 1) = 2An
So {an} is the common ratio q = 2
Because the first term is A0 = 1
So the general formula an = 2 ^ n
But I think the first item of {an} is from A1
If A1 = 1, then the general formula an = 2 ^ (n-1)

Try to write at least two polynomials that only contain the letters X and y, and satisfy the following conditions: (1) cubic polynomial; (2) coefficient of each term is 1 or - 1; (3) no constant term; (4) each term must contain both the letters X and y, but no other letters

The answer to this question is not unique, such as: x3y3-x2y4 + xy5; - x2y4-xy-xy2

A barrel of oil weighs 55.4kg. After half use, the barrel weighs 30.2kg. How much is the oil? How much is the barrel?

55.4-30.2=25.2
25.2 * 2 = 50.4 (oil weight)
55.4-50.4 = 5 (barrel weight)

If f (x) = sin α - cosx, then f '(α) is equal to?
Why is f '(x) equal to SiNx? I don't understand that.

f（x）=sinα-cosx
So f '(x) = SiNx
So f '(α) = sin α

Solution scale (equation calculation)
Tractor ploughs a piece of land, 0.6 hectares per day, 5 days to finish. If 4 days to finish, how many hectares per day? (equation)
The tractor ploughs a piece of land, 0.6 hectare per day, and it can be finished in 5 days. If 0.75 hectare per day, how many days can it be finished? (equation)
Zhiming walked 300 meters in 5 minutes. At this speed, he walked 12 minutes from home to school. How many meters is Zhiming's home from school? (equation)
Xiaomei uses her savings to buy pencils. If she buys 0.2 yuan, she can buy 12 pencils. If she buys 0.3 pencils, how many pencils can she buy
The turnover of Jianbu shopping mall in five days reaches 42000 yuan. According to this calculation, how many yuan is the estimated turnover in one month (30 days)
Students practice, each line stands 18 people, just stands 32 lines. If each line stands 24 people, how many lines can stand? (equation)
Use a sum of money to buy cloth. If you buy cloth that costs 13.5 yuan per meter, you can buy 6 meters. If you buy cloth that costs 10.8 yuan per meter, how many meters can you buy? (equation)

1. If the cultivated land is x hectares per day, 4x = 0.6 × 5 = > x = 0.75 hectares
2. 75 x = 0. 6 × 5 = > x = 4 days
3. The school is x meters away from home, X / 12 = 300 / 5 = > x = 720 meters
4. Let x = 0.3x = 0.2 × 12 = > x = 8
5. Suppose that the turnover of a month can reach x 10000 yuan, X / 30 = 4.2 / 5 = > x = 252000 yuan
6. Let x station row 32 × 18 = 24x = > x = 24 rows
7. Let x meter cloth 13.5 × 6 = 10.8x = > x = 7.5m