If B ^ 2 = a C = 9, then B is equal to 3 or a 3, there is only one answer

If B ^ 2 = a C = 9, then B is equal to 3 or a 3, there is only one answer

The answer is - 3. First of all, the above five numbers are in equal proportion, so this ratio is two choices: positive and negative. If it is positive, then all numbers should be negative. If the equal ratio is negative, then AC is positive, B is negative, so choose - 3

If any one of the items of an equal ratio sequence is equal to the sum of the following two items, then its common ratio is ()
A. − 1 − 52b. − 1 + 52C. 1 + 52d. − 1 − 52 or − 1 + 52

From the meaning of the title, we can get an = an + 1 + an + 2, ∵ an + 1 = anq, an + 2 = anq2, ∵ an = anq + anq2, ∵ an > 0, ∵ 1 = q + Q2, and the solution is q = − 1 ± 52, ∵ Q > 0, ∵ q = 5 − 12

The distance between city a and city B is 560 km. The two trains leave from city a and city B at the same time and meet in 3.5 hours. Car a travels 85 km per hour, and how many km per hour does car B travel?

560 △ 3.5-85, = 160-85, = 75 (km); answer: car B travels 75 km per hour

If the average of a group of data - 1, - 2, x, 1, 2 is 0, then the variance of this group of data is 0______ ．

From the formula of the average, (- 1-2 + 1 + 2 + x) △ 5 = 0, the solution is x = 0; the variance = [(- 1-0) 2 + (- 2-0) 2 + (0-0) 2 + (1-0) 2 + (2-0) 2] △ 5 = 2

The distance between a and B is 280 kilometers. A car from a to B runs 150 kilometers in three hours. At this speed, the rest of the journey will take several hours
To judge the formula, what divided by what equals what, what must be. Or what multiplied by what, what must be

150 △ 3 = 50 (km / h), the speed is constant, and the ratio of distance to time is constant
It will take another x hours
150：3=(280-150)：x
X = (280-150) × 3 / 150 = 2.6 (hours)
The rest of the journey will take 2.6 hours

A perfect square n, plus 1999 or a perfect square, what is the number?

(n+1)^2=n^2+2n+1
2n+1=1999
n=999

A and B leave from a and B at the same time. When they meet for the first time, they are 90 kilometers away from a station. After passing, they continue to move forward at the same speed and reach the opposite station respectively
The distance between a and B is 13 / 20 of the distance between a and B. how many kilometers is the distance between a and B?

90×3÷（1+1-13/20）
=270÷27/40
=400 km

Let o be the center of the square ABCD, the quadrilateral odef be a parallelogram, and the plane odef ⊥ plane ABCD, if ad = 2, de = 2. (I) prove whether there is a point m on the line EC of the FD ⊥ plane ace. (II) make the AE ∥ plane BDM? If it exists, find the value of EM: MC; if not, explain the reason

(I) in square ABCD, BD ⊥ AC, ≁ ad = 2, ≁ BD = 22, OD = 2, ≁ de = OD, ≁ parallelogram odef is rhombic, ≁ FD ⊥ OE, and ≁ plane odef ⊥ plane ABCD, ≁ AC ⊥ plane odef, ≁ AC ⊥ DF, while AC ∩ OD = O, ∩ FD ⊥ plane ace; (II) there is a midpoint m of line EC, so that

For a pile of coal, the ratio of tons transported in the first day to the total tons is 1:4. After 4.5 tons were transported in the second day, 23% of the total coal was transported in two days. How many tons of coal are there in this pile?

A: there are 10.8 tons of coal in this pile

Using mean inequality to find the maximum value of function
Given that a and B are constants, find the minimum value of F (x) = (x-a) ^ 2 + (X-B) ^ 2