① . A and B are two natural numbers (not equal to 0). If 5 / 6 of a is 1 / 4 of B, what is the minimum sum of a and B? ② 12:5 hours = () minutes 7500 square meters = () hectares ③. There is the largest circle in a square. If the square area is 20 square centimeters, what is the area of the circle? (formula) ④. How many grams of water need to be added to 20 grams of salt to prepare salt water with 10% salt content? (formula) ⑤. Xinhua bookstore has a new batch of children's books, and sold 3 / 8 of the total on the first day, The next day, 40% of the total number of children's books were sold, and 450 copies remained. How many of these children's books are there?

① 5 / 6 of a is 1 / 4 of B, so a: B = 1 / 4:5 / 6 = 3:10. Because a and B are both natural numbers, the minimum value of a + B is 13. 2. 5 / 12 hours = (25) minutes 7500 square meters = (0.75) hectares. 3. The diameter of the largest circle in a square is equal to the side length of the square, that is (root 20) cm, so the area of the circle

If a ≥ 0 and the solution of the equation a + 2x = 2 is a natural number, what is the value of a

Because a + 2x = 2
So x = (2-A) / 2 > = 0,
So 0

F (x) = (n power of x-n power of x) / N power of X + n power of X, n ∈ n +,
Try to compare the size of F (radical 2) and (n & # 178; - 1) / (n & # 178; + 1), explain the reason (feel like using mathematical induction) to help

F (x) = x ^ N-X ^ - N / x ^ n + x ^ - n = (x ^ 2n-1) / (x ^ 2n + 1) = 1-2 / (x ^ 2n + 1) this is a decreasing function
F (radical 2) = 1-2 / (2 ^ n + 1)
And (n ^ 2-1) / (n ^ 2 + 1) = 1-2 / (n ^ 2 + 1) can be regarded as the function value when x = n ^ 2
Next, just compare the sizes of 2 ^ n and n ^ 2
If n = 2 or 4 is equal, 2 ^ n = n ^ 2, so f (radical 2) = (n ^ 2-1) / (n ^ 2 + 1)
When n = 1 or n > 4, 2 ^ n > n ^ 2, Suoyi)
F (radical 2)

If n is an integer, can n & # 178; + n be divisible by 2? Please explain why

Yes, reason:
n²+n=n(n+1)
These are two continuous natural numbers, of which there must be an even number;
Therefore, n & # 178; + n can be divisible by 2

On the distance between the point on the ellipse and the focus
The distance from a point P on the ellipse (X & sup2 / 169) + (Y & sup2 / 144) = 1 to the right focus is 5. The correct conclusion in the following is ()
A: The distance from P to left focus is 21. B: the distance from P to left focus is 8
C: The distance from P to the left focus is uncertain. D: such a point P exists

It is known that a = 13,
According to the definition of ellipse: the sum of the distances from the point on the ellipse to the two focal points is equal to 2a, the distance from the point P to the left focal point is 21, which seems to choose a
The intersection of the ellipse and the positive half axis of X axis is (13,0), while the right focus is (5,0), which means that the minimum distance from the point on the ellipse to the focus is 8, so there is no such point P

24 can be written as the sum of which two primes? How different is it? There should be an expression

24=5+19
24=7+17
24=11+13

What is the domain of the function y = logx-1 to the power of 3-x

Base X-1 > 0, x > 1
And X-1 ≠ 1, X ≠ 2
True 3-x > 0
x

When the sign of the positive scale function y = KX is the same as that of the inverse scale function K, the two intersections are symmetric with respect to the origin?
When the sign of the positive scale function y = KX is the same as that of the inverse scale function K, two images must have intersections, and two images have two intersections, which are symmetric about the origin or the center
Is this sentence correct? Why? How can we prove it?
＠ if it is established, can it be used directly? ＠＠

Inverse function: y = K / X
By introducing y = KX into y = K / x, we can get x = + / - 1,
Then y = KX is taken in to obtain the coordinates of two intersections, which are (1, K) and (- 1, - K)
So it's symmetrical about the origin

The number axis represents two points of X and - 2. The distance between a and B is (). If | ab | = 3, then x = ()

The number axis represents two points of X and - 2. The distance between a and B is (| x + 2 |). If | ab | = 3, then x = - 5,1

What does it mean that the lower right corner XY of ρ in probability theory is equal to 0.4

Probability of xy = 0.4