In the arithmetic sequence an, we know A1 = 3 / 2, d = - 1 / 2, Sn = - 15, find the sum of N and an

In the arithmetic sequence an, we know A1 = 3 / 2, d = - 1 / 2, Sn = - 15, find the sum of N and an

According to the summation formula of arithmetic sequence:
Sn=a1*n+n*(n-1)*d/2
Substitution number - 15 = 3 / 2 * n + n * (n-1) * (- 1 / 2) / 2
Reduction, n ^ 2-7n-60 = 0,
The solution is n = - 5 (rounding off), n = 12
So n = 12
an=a1+(n-1)*d =3/2+(n-1)*(-1/2)=-1/2n+2

"B & # 178; = AC" is the () condition for a, B, C to be an equal ratio sequence

Necessary conditions
Because, if a, B, C are equal ratio sequence, then B ^ 2 = AC
But when a = b = 0, there is always b ^ 2 = AC, and a, B, C are not equal proportion sequence
In conclusion, B ^ 2 = AC is a necessary condition for a, B, C to be an equal ratio sequence

2yz/x+2xz/y+2xy/z≥2x+2y+2z

XYZ(2yz/x+2xz/y+2xy/z)/XYZ=(2Y^2Z^2+2X^2Y^2+2X^2Z^2)/XYZ
=(Y^2Z^2+X^2Y^2+X^2Z^2+Y^2Z^2+X^2Y^2+X^2Z^2)/XYZ
>=(2XYZ^2+2XZY^2+2YZX^2)/XYZ
=2X+2Y+2Z

The sum of the two numbers a and B is 23.126. If the decimal point of a is moved one place to the left, the number obtained is three times that of B, then the number a is 23.126______ ．

The total number of copies: 30 + 1 = 31 (copies), the number of a is: 23.126 × 3031 = 22.38; so the answer is: 22.38

If the rational number XY satisfies the equation (1 / 2 + √ 2 / 3) x + (1 / 3 + √ 2 / 2) y = 4 + √ 2, then X-Y =?

∵(1/2+√2/3)x+(1/3+√2/2)y=4+√2
==>x/2+√2x/3+y/3+√2y/2=4+√2
∴(x/2+y/3)+(x/3+y/2)√2=4+√2
∵ X and y are rational numbers
∴x/2+y/3=4,x/3+y/2=1
==>3x+2y=24,.(1),2x+3y=6.(2)
Therefore, from formula (1) to formula (2), X-Y = 18

The green team planted 500 trees, 20 of which did not survive. What is the survival rate of these trees?
No need to think about it

(500-20)/500=96%

Solving inequality lx-2l + LX + 3L ≥ 4

Classified discussion
1 x less than - 3 2-x-x-3 > = 4
2 x > 2 X-2 + X + 3 > = 4
3 - 3 less than x less than 2 2 - x + X + 3 > = 4
Then we take the union

Xiaoming spent 16 yuan on three bottles of a drink and four bottles of B drink in the supermarket. The unit price of B drink is 0.5 yuan higher than that of a drink

Suppose the unit price of drink a is x yuan, then the unit price of drink B is (x + 0.5) yuan
So 3x + 4 (x + 0.5) = 16
X=2
So the unit price of a is 2 yuan and that of B is 2.5 yuan

How to solve the equation 1A + 3A = 40?

1A + 3A = 40
10 out of 3 a = 40
a=40×3/10
a=12

At 8:00 yesterday, a truck drove from a to B, at 9:00, a car drove from B to a, at 11:00, the two cars just met at the midpoint of the distance between a and B, and the car traveled 120 km per hour. If there was no accident, when did the truck arrive at B yesterday? How fast is the truck?

(1) 11:00-8:00 = 3 (hours), 11:00-9:00 = 2 (hours), 11:00 + 3 hours = 14:00; (2) 120 × 2 = 240 (kilometers), 240 ／ 3 = 80 (kilometers); a: the truck arrived in the second place at 14:00 yesterday, and the speed of the truck was 80 kilometers per hour