In the arithmetic sequence {an}, A1 = 6, branch 5, tolerance d = - 6, branch 1, if the sum of the first n terms Sn = - 5, find the number of terms n

In the arithmetic sequence {an}, A1 = 6, branch 5, tolerance d = - 6, branch 1, if the sum of the first n terms Sn = - 5, find the number of terms n

an=5/6-1/6(n-1)=(6-n)/6
So Sn = (a1 + an) n / 2 = [(11-n) / 6] n / 2 = - 5
n²-11n-60=0
(n-15)(n+4)=0
So n = 15
Some materials will lose their resistance at low temperature and become superconductors. When the current passes through, the voltage at both ends of the superconductor is? And the electric power is?
Are they all zero? Why
There is a problem with the problem. At ultra-low temperature, the resistance does not disappear, but becomes very small. If the resistance is small, its power consumption is very small. That is, I * IR is very small. This is the electric power. In addition, the voltage at both ends is also very small
The higher the resistance, the higher the voltage at both ends, the resistance will disappear and become superconductor, the voltage is 0
The superconductor can be connected into a circuit by itself after being electrified, and there will still be continuous current in it without attenuation. Of course, this is the ideal situation, that is, the resistance is 0. In fact, there is current attenuation, but the speed is very slow, and it usually does not decay one milliampere a year, which means that there is a very small resistance. The resistivity of superconductors is below the order of 10 ^ - 24, but it is not equal to 0. ... unfold
The superconductor can be connected into a circuit by itself after being electrified, and there will still be continuous current in it without attenuation. Of course, this is the ideal situation, that is, the resistance is 0. In fact, there is current attenuation, but the speed is very slow, and it usually does not decay one milliampere a year, which means that there is a very small resistance. The resistivity of superconductors is below the order of 10 ^ - 24, but it is not equal to 0. Put it away
Superconductivity is that the resistance is 0, the ideal wire does not consume electric power, the electric power is 0, the voltage at both ends is equal
The area of a triangle is represented by the letter formula
Suppose there is a triangle with side lengths a, B and C respectively. The area s of the triangle can be obtained by the following formula:
S=√[p(p-a)(p-b)(p-c)]
In the formula, P is the half perimeter
p=(a+b+c)/2
The tolerance of the arithmetic sequence {an} is D, Sn = - n ˇ 2, and the general term formula of the sequence is obtained
Sn=-n^2
When n = 1, A1 = - 1
When ^ 2 N + = 2 n-1
When n = 1, the upper expression holds
The general formula of the sequence is an = 1-2n
About electric power calculation
L1 220V 40W L2 220V 100W
They are connected in parallel with 110V power supply, and their actual power consumption is calculated?
Known: L1 220V 40W, L2 220V 100W, u = 110V, calculate: (1) actual power consumed by L1; (2) actual power consumed by L2. (1) p1 = U1 * U1 / R1 = u * U / P = 1210 Ω P real 1 = u * U / r = 110V * 110V / 1210 Ω = 10W (2) P2 = U2 * U2 / r2 = u * U / P = 484 Ω P real 2 = u * U / r = 110V * 110V / 484
Find the resistance first. If the voltage is constant, then calculate the current they divide.
P = UI, that's good. Sorry, I don't have time today. Think about it for yourself
The simplest U1 / 2 = P1 / 4
The base of a triangle has a length a, a height h and an area ()
1/2ah
Multiply a by H
This question should be asked about textbooks. Don't you think it's faster to turn over books??? The basic theorem
A times h and divide by 2
Half bottom by half height
The known sequence {an} is an arithmetic sequence with the first term of 1 and the tolerance of 2. The sum of the first n terms is SN. The general term formula is obtained
It is known that the sequence {an} is an arithmetic sequence with the first term of 1 and the tolerance of 2, and the sum of the first n terms is SN. 1. Find the general term formula an and Sn? 2, let CN = BN an, where the sequence {CN} is an arithmetic sequence with the first term of 1 and the common ratio of 3. Find the general term formula of the sequence {BN} and its first n terms and TN? 2?
(1) According to the formula of the sum of the first n terms of an arithmetic sequence, Sn = (1 + 2n-1) * n / 2 = n & # 178; (2) CN = 3 ^ (n-1) = BN an, that is, BN = 3 ^ (n-1) + 2n-1tn, the first n terms of CN and TN = (1-3 ^ n) / (1-3) + n & # 178; = (3 ^ n + 2n & # 178; - 1) / 2 can be obtained separately
1)an=1+(n-1)2=2n-1 Sn=n+n*2-n=n*2
2)bn=3*(n-1)+2n-1 Tn=-0.5(1-3*(n-1))+n*2
Because A1 = 1, d = 2
∴An=2n-1
The general term is: SN = (1 + 2n-1) * n / 2 = n ^ 2
C1=1 , q=3
∴Cn=3^(n-1)
So BN = CN + an = 2N-1 + [3 ^ (n-1)]
Tn=(n^2) +(3/2)[(3^n)-1]
Electric power and safe use of electricity, a short answer
In the lighting circuit of Xiaolin school, the fuse at the main switch often blows inexplicably (there is no fault in the circuit), and it is usually broken at the top of the fuse. After the fuse is replaced according to the requirements, it will not last long. Sometimes, even if a larger fuse is replaced, the frequent power failure can not be changed, especially in summer, This kind of fuse "allergy" phenomenon is more likely to occur. Can you analyze the causes and find solutions according to the knowledge you have learned?
In summer, there are many electrical appliances, and the electrical appliances are all in parallel. The characteristic of parallel circuit is that the smaller the resistance is, the greater the total current in the main circuit will be when the voltage of the transmission line remains unchanged (220 V). When the fuse is connected in the main circuit, the power consumed by the fuse will increase when the current is too large (P = I ^ 2 / R --- the derivation formula of electric power), The heat produced also increases (q = I ^ 2 · R · t -------- Joule's law). If it exceeds the limit, the fuse will blow
In the triangle area formula s = 1 / 2 h, if a is fixed and H is an independent variable, then 1 / 2 A is a constant____ Quantity s follows___ Change with the change of time
In the triangle area formula s = 1 / 2 h, if a is fixed and H is an independent variable, then 1 / 2 A is a constant__ Change_ Quantity s follows_ Independent variable H__ Change with the change of time
The first term A1 = 3 of sequence {an} is known, and the general term an satisfies 2An = snsn-1 (n ≥ 2) with the first n terms and Sn. (1) prove that {1sn} is an arithmetic sequence and find the tolerance; (2) find the general term formula of sequence {an}
(1) ∵ 2An = snsn-1 (n ≥ 2) ∵ 2 (sn-sn-1) = both sides of snsn-1 are divided by snsn-1 at the same time, and 2 (1sn-1-1sn) = 1 ∵ 1sn-1sn-1 = - 12 ∵ 1sn} is an arithmetic sequence, and the tolerance d = - 12 (2) ∵ 1S1 = 1A1 = 13 ∵ 1sn = 13 + (n-1) × (- 12) = - 12n + 56 = 5-3n6 ∵ Sn = 65-3n. When n ≥ 2, an =