There are 84 students in class A and class B. 20% of them are transferred from Class A to class B, and then 2 students are transferred from class B to class A. at this time, the number of students in the two classes is exactly the same

There are 84 students in class A and class B. 20% of them are transferred from Class A to class B, and then 2 students are transferred from class B to class A. at this time, the number of students in the two classes is exactly the same

84 △ 2 = 42 (people); 42-2 = 40 (people); 40 △ 1-20%, = 40 △ 80%, = 50 (people); 84-50 = 34 (people); a: there were 50 people in class A and 34 people in class B

The total number of students in a school is 450, and the proportion of students in three grades is 2:3:4

First grade 450 * 2 / 9 = 100
Second grade 450 * 3 / 9 = 150 (people)
Grade 3 450 * 4 / 9 = 200
The number of students in the highest grade is 200

log2（x-4）=log4(15-x)+1

X = 2 + 4 radical 3

The inscribed circle O of △ ABC cuts three sides with D, e and F, if ∠ a = 60 °, BC = 5, AB + AC = 11
Verification
(2) Find the radius of ⊙ o
(3) Find the area of △ ABC
Sorry, wrong number
And the one on the first floor is wrong
1.5；12
I want to ask how to solve the problem

√3,8√3

How does inequality transform symbols

To remove a negative sign or multiply by a negative value is to change the sign
For example:
(1) -4x≤1
4x≥-1
(2) 3x+1≥5
3x≥4

Hanyu Pinyin: do w and u, y and I sound exactly the same?

In Chinese Pinyin, u and I are the finals, while W and y are just the letters that play a sound insulation role in spelling. The reason why many people think that w, u, y and I have the same pronunciation is that they do not understand the spelling rules of Pinyin. For example, "Yi" is written as "Yi" in pinyin. In fact, only "I" has a pronunciation, In order that words like "coat" will not be confused with "Dai" in pinyin, so y and W are not initials and have no pronunciation
For example, "Yu" is written as "Yu" because "Y" is always added before the vowel V (adding two points to u when handwritten), and the two points on V are omitted

A problem of analytic geometry in Senior High School
It is known that the two ends of the major axis of the ellipse C: x2 / A2 + Y2 / B2 = 1 (a > b > 1) are A.B. if there is a point P on the ellipse, the angle APB is 120 degrees. The range of eccentricity of the ellipse is obtained
Seeking specific process and answer

Soy sauce purple
Think about it first: if there is a point P on an ellipse, the maximum value of the angle PAB is the value of the angle PAB when the point P is on the Y axis. Therefore, "if there is a point P on the ellipse, the angle APB = 120 degrees" means that the angle PAB is equal to 120 degrees
Let the intersection of the ellipse and the y-axis be p, a focus of the ellipse on the x-axis be f, and o be the origin
Then | PF | = a, | of | = C, eccentricity e = C / A
Obviously e = | of / | PF | = cos (angle PAB / 2)
When the angle PAB is 120 degrees, cos (angle PAB / 2) = cos60
Because the angle PAB > = 120 degrees
So half of the angle PAB > = 60 degrees
So e

Who can help me with these four operations
Can you help me work out the answers to these four operations
It's good to count 126, and you can add 40 points

If the equation x ^ 2-2x + A-8 = 0 has two real roots x1, X2, and x1 ≥ 3, X2 ≤ 1, find the range of A

Delta = 4-4 (A-8) > = 0, then a

If the ratio of length to width of the inscribed rectangle of ellipse x ^ 2 / 9 + y ^ 2 / 18 = 1 is 3:2, then the area of the rectangle is?

The focus is on the y-axis. If the short side of the inscribed rectangle is parallel to the x-axis, let the coordinates of a vertex of the rectangle be (2m, 3M), (2m) ^ 2 / 9 + (3m) ^ 2 / 18 = 1, M = 3 √ 34 / 17, the length of the short side is 12 √ 34 / 17, the length of the long side is 18 √ 34 / 17, area: (12 √ 34 / 17) * (18 √ 34 / 17) = 432 / 17. If the long side is parallel to the x-axis, (3m) ^ 2 / 9 + (2m) ^ 2 / 18 = 1, M =