The mass of the wooden ball is 1 / 2 of that of the iron ball, and the radius of the wooden ball is twice that of the iron ball (both balls are solid). How many times is the density of the wooden ball (it's better to talk about the volume ratio)

v=4/3pi*r^3
p=m/v=m/(4/3pi*r^3)
V wood / V iron = (r wood / R iron) ^ 3 = 8
P wood / P iron = m wood / M iron / (r wood / R iron) ^ 3 = 1 / 2 / 8 = 1 / 16

If the volume ratio of two iron balls is 2:1, then the density ratio and the mass ratio of the two iron balls are?

The density ratio is 1:1, the mass ratio is 2:1

The first n terms of sequence {an} and Sn = a ^ n + B (a, B are constants and a is not equal to 0,1) ask whether sequence {an} is an equal ratio sequence, if write the general term formula
A1 = S1 = a + B, when n > = 2, an = sn-sn-1 = (A-1) a ^ (n-1), and A1 = (A-1) a ^ 0 = A-1, therefore, if A-1 is not equal to a + B, that is, B is not equal to - 1, it is obvious that the sequence {an} is not an equal ratio sequence; if A-1 = a + B, that is, B = - 1, from an = (A-1) a ^ (n-1) (n > = 1), we can get an / (an-1) = a (n > = 2) why a + 1 is compared with a + B, it is obviously not equal ratio (n > = 1) (n > = 2). Please don't bother to help me
I don't understand why it compares a + 1 with a + B, and how it can clearly see that it is not an equal ratio sequence, and what the last (n > = 1) and (n > = 2) are for. Please don't be bothered. I hope you can help me. If you can prove it, please prove that an = sn-sn-1 = (A-1) a ^ (n-1). This is when n > = 2, why does it substitute 1 in and out, and make A1 = A-1

According to the question meaning: A1 = S1 = a + B, when n > = 2, an = sn-sn-1 = (A-1) a ^ (n-1), R, so A2 = (A-1) A. if it is an equal ratio sequence, then the second term divided by the first term should also be equal ratio common ratio a. the common ratio is a, so there should be A1 * common ratio = the second term, that is, (a + b) a = (A-1) A. since a is not equal to 0, we have to let B = - 1
If it is an equal ratio sequence, then the general term formula is unified, that is to say, it holds for any n, and there is no n > = 2 restriction. Under this condition, the first term should be the value when n = 1. Then compare this with the condition of the title itself, and finally get b = - 1. Here, it is reverse thinking

Use a piece of iron wire to form a square with a side length of 6.28cm. If you use this piece of iron wire to form a circle, what is the area of the circle?

Radius = 6.28 × 4 ﹣ 3.14 ﹣ 2 = 4cm
Area = 4 × 4 × 3.14 = 50.24 square centimeter

4.17-4.17 = simple calculation

=(101—1)x4.17=100x4.17=417

Given that the variance of data X1 and X2 is S2, then the variance of data X1 + B and X2 + B is S2______ ．

The original variance S2 = 12 [(x1 -. X) 2 + (X2 -. X) 2] = S2, the current variance s'2 = 12 [(x1 + B -. X-B) 2 + (x2 + B -. X-B) 2] = 12 [(x1 -. X) 2 + (X2 -. X) 2] = S2, the variance does not change

Living room area is 38.2 square meters, if the side length is 0.5 meters square tiles, 150 such tiles enough

0.5*.05=2.5
150*2.5=37.5
(bracket --- because there is an extra loss rate of the corner and corner, it needs 155 yuan
The answer is not enough---

If x > 0, Y > 0, xy = 6, then the minimum value of 3x + 2Y?

x> 0, Y > 0, xy = 6, then the minimum value of 3x + 2Y?
3x + 2Y > = 2 * radical (3x * 2Y) = 2 * radical 6xy
>= 2*6
》=12
So the minimum value is 12

Arcsinx + arccosx is equal to 90 degrees, please

Let y = arcsinx + arccosx, y '= 1 / √ (1-x ^ 2) - 1 / √ (1-x ^ 2) = 0, then y = arcsinx + arccosx = constant, y = arcsin0 + arccos0 = 0 + π / 2 = π / 2

The edge length of the large cube is twice that of the small cube, and the volume of the large cube is 21 cubic decimeters more than that of the small cube. What is the volume of the small cube?

21 (8-1) = 3 (cubic decimeter), a: the volume of small cube is 3 cubic decimeter

The mass of the wooden ball is 1 / 2 of that of the iron ball, and the radius of the wooden ball is twice that of the iron ball (both balls are solid). How many times is the density of the wooden ball (it's better to talk about the volume ratio)