It is known that the equation x2 + (A-3) x + 3 = 0 has a constant solution in the range of real number, and there is just one solution greater than 1 and less than 2, and the value range of a is______ ．

It is known that the equation x2 + (A-3) x + 3 = 0 has a constant solution in the range of real number, and there is just one solution greater than 1 and less than 2, and the value range of a is______ ．

Let f (x) = x2 + (A-3) x + 3, the problem is equivalent to that f (x) has a zero point in (1,2) according to the distribution of roots of quadratic equation, which is equivalent to If [1 + (a-3-3) 2 [4 + (a-3-3) 2 + 3] or [1 + (a-3-3) (a-3-3) 2 [4 + (a-3-3) 2 + 3] < 0 or [1 + (a-3-3-3) + [1 + (a-3-3) + [1 + (a-3-3) - 3] [(4 + (a-3-3) 2 (4 + (A-3) 2 (2) < 0 or (f (a + 1) [(a-1-1-12 or a-1-1 or A-1 or a-12-1 or a-12-12-1 or a-12-12-12-12-12, when △ 0, that is b2-4ac ≥ 0, that is b2-4ac ≥ 0, b2-4ac ≥ 0, b2-4ac ≥ 0, [(a-4-4-4-4-4-4ac ≥ 0, [(a-3-3-3-< a ≤ -So the answer is: - 1 < a ≤ - 23 + 3

Given the function f (x) = ① X-1, X ＞ 0, ② 3 ^ x, X ≤ 0, if the equation f (x) + x-a = 0 about X always has 2 solutions, then the value range of real number a?

Let y = f (x) + X
x> 0, y = X-1 + x = 2x-1, then monotonically increasing, Y > - 1
x

Given that the equation f (x) = | x-3x + 2 | - M has four zeros, then the value range of real number m is_____

f(x)=|x²-3x+2|-m=|(x-2)(x-1)|-m
If there are four zeros, then M > 0
We can see by drawing
|(X-2) (x-1) | there is a point (3 / 2,1 / 4) which is the extremum
m

It is known that a = {2A + 1

If a is included in (a ∩ b), then a ∩ B = a
That is, a is contained in B
So 2A + 1 ≥ 13 and 3a-5 ≤ 22
So 6 ≤ a ≤ 9
That is, set M = {a | 6 ≤ a ≤ 9}

In the Three Gorges, the sentence embodying the length of the Three Gorges is ()

From the seven hundred Li middle of the Three Gorges http://www.baidu.com/s?kw=&sc=web&cl=3&tn=sitehao123&ct=0&rn=&lm=&ie=gb2312&rs2=&myselectvalue=&f=&pv=&z=&from=&word=%A1%B6%C8%FD%CF%BF%A1%B7%D6%D0%A3%AC%CC%E5%CF%D6%C8%FD%CF%BF%B3%A4%B5...

How many terms should be expanded by Taylor formula
 
As shown in the figure, the number of expanded items in question 1, question 2, question 3 is not the same. How to see how many items to expand, especially questions 2 and 3;
 
OS: I know how many items are open to the power of the unknown, but I can't see questions 2 and 3
 
 

The Taylor expansion method is used to find the limit. You have to get the lowest order term accurately before you can stop
If the number of items is less, the embarrassing situation will appear
In order to avoid this situation, we need to expand several terms until the lowest order term can be calculated accurately
I hope my answer can help you~

The number of boys is five ninths of the class, so the number of girls is four fifths of the number of boys, right or wrong

That's right. The number of boys is 5 / 9 of the class, and the number of girls is 4 / 9. If the denominator is the same, it can be omitted, which means that the ratio of boys to girls is 5:4, then the number of girls is 4 / 5 of boys
Let's take an example. Suppose there are 9 students, 5 boys and 4 girls
4 △ 5 = four fifths
yes.
Pure hand

84.2 × 1.27 △ 4.21 simple method 3.69 × 31.5 △ 10.5 simple method

84.2×1.27÷4.21
=（84.2÷4.21）×1.27
=20×1.27
=25.4
3.69×31.5÷10.5
=3.69×（31.5÷10.5）
=3.69×3
=（3.7-0.01）×3
=3.7×3-0.01×3
=11.1-0.03
=11.07

Do all sequences have general term formulas? For example, - 1,2,3, - 4,5,6, - 7,8,9, - 10 Is there a general term formula? What is it?

1. Not all series have general term formula. For example, if an = the nth decimal of PI, the series {an} has no general term formula
2 - 1,2,3, - 4,5,6, - 7... Has a general formula, which is an = n * (- 1) ^ xn
Where xn = n - 3 * [n / 3], where [] is an integer function

What is the sum of 7 times of 0.8 and 1.2

7*0.8+1.2*1.5
=5.6+1.8
=7.4
Do not understand, welcome to ask!
Hope to adopt, thank you!