In the sequence {an}, A1 = 13 and Sn = n (2n-1) an, the expression of an () A. 1(n−1)(n+1)B. 12n(2n+1)C. 1(2n−1)(2n+1)D. 1(2n+1)(2n+2)

In the sequence {an}, A1 = 13 and Sn = n (2n-1) an, the expression of an () A. 1(n−1)(n+1)B. 12n(2n+1)C. 1(2n−1)(2n+1)D. 1(2n+1)(2n+2)

From A1 = 13, Sn = n (2n-1) an, S2 = 2 (2 × 2-1) A2, i.e. a1 + A2 = 6A2, A2 = 115 = 13 × 5, S3 = 3 (2 × 3-1) A3, i.e. 13 + 115 + a3 = 15a3, A3 = 135 = 15 × 7, A4 = 17 × 9. Therefore, an = 1 (2n − 1) (2n + 1) is conjectured
In a series circuit, there are two resistors. When one of them becomes larger, how does the electric power on it change
Is the electrical power on the resistor
Some students asked me, hee hee could not answer
1. The total voltage on the circuit remains unchanged
Voltage u, current I, resistance R, R,
The power of R is p = I & sup2; r = u & sup2; / (R + R) & sup2; R
The power variation of R △ P = P ′ - P = u & sup2; R ′ / (R + R ′) & sup2; - U & sup2; R / (R + R) & sup2;
=[U² /((r+R′) ² (r+R) ²]*[R’(r+R) ²-R(r+R′) ²]
U & sup2; / ((R + R ') & sup2; (R + R) & sup2; is always greater than zero, so we only need to judge whether R' (R + R) & sup2; - R (R + R ') & sup2; is greater than zero,
When R '(R + R) & sup2; - R (R + R') & sup2; > 0, R ′
Smaller
Electric power is related to voltage and current. When the resistance in a series circuit increases. It is determined that the voltage applied to the circuit is constant. The electric power decreases. There is no definite condition factor in the question. So the answer is a little vague. ha-ha
You make a formula, according to the mathematical analysis, I remember everything!
reduce
It is known that the perimeter of triangle is YCM and the lengths of three sides are 2cm, 5cm and xcm respectively. What is the functional relationship between Y and X and what is the value range of independent variable x
The function formula is: y = x + 7. The value range of self variable is: 3 less than x less than 7
y=x+2+5。
So the function relation is y = x + 7
According to the relationship between the length of triangle sides
X5-2 (the difference between the two sides is less than the third side)
The value range of X is: 3
Given the first n terms of the sequence {an} and Sn = 1-2 / 3an, (1) calculate A1, A2, A3 (2) find the general term formula of an according to the calculation, and prove it by the method of number reduction
(3) Finding the limit of Liman and limsn
Can you make that recursion more clear
In series circuit, the ratio of voltage, current, resistance to electric power and power
In series circuit, the ratio of voltage, electric power and electric power is equal to the ratio of resistance except current
U1/U2=W1/W2=P1/P2=R1/R2=Q1/Q2
(voltage, electric power, electric power, resistance, electric heating)
And I1 = I2 (current)
In the DC series circuit, the voltage is proportional to the resistance, the current is equal to the main circuit current, and the ratio of electric power to electric work is p = I ^ 2 * r. we can know that it is also proportional to the resistance
In series circuit, w = P * t, P = (U1 + U2) * I,
Because u = IR, series circuit I1 = I2,
So p = (IR1 + IR2) I = (R1 + R2) * I ＾ 2
W=UIT=I^2RT=PT
U=IR
P=UI
R=（U^2）/P
It is known that the base of the triangle is 4 cm long, x cm high, and the area of the triangle is y cm square
solution
y=1/2*4*x=2x
This is a linear function
Function image is a straight line, you just need to find two points to connect it
You draw your own axis, point (0,0) and point (1,2)
Then connect the two points with a ruler and extend them
If the sum of the first n terms of the sequence an is Sn = 2 / 3an-3, then the general term formula is
It's 3 / 2An
Sn=3/2An-3 （1）
S（n-1）=3/2A（n-1）-3 （2）
（1）-（2） Sn-S（n-1）=3/2An-3/2A（n-1）
An=3/2An-3/2A（n-1）
An=3A（n-1）
An=A1*3^(n-1)
Because A1 = 3 / 2a1-3
So A1 = 6
So an = 6 * 3 ^ (n-1) = 2 * 3 ^ n
Is series circuit high resistance and low power
According to P = I2R, is the electric power with large resistance also large?
But if the current is large, isn't the power also large?
P = I2R, P = U2 / R is only applicable to pure resistance circuit, whether in series or in parallel, the total power consumed in the circuit is equal to the sum of the power consumed by various electrical appliances. The distribution of electric power in series circuit: because P1 = iu1, P2 = iu2, P1: P2 = iu1: iu2 = U1: U2, P1: P2 = R1: R2, because U1: U2 = R1: R2
That is, the distribution of electric power in series circuit is proportional to the resistance
Because P1 = i1u, P2 = i2u, P1: P2 = i1u: i2u = I1: I2, because I1: I2 = R2: R1, P1: P2 = R2: R1, the distribution of electric power in parallel circuit is inversely proportional to the resistance
Therefore, the power of series resistance is higher than that of parallel circuit
Series connection is a circuit with high resistance and low power
Because as the resistance increases, the current decreases,
For example, if the resistance is doubled, the current will be 1 / 2 of the original
If P = I2R is used, the electric power will be 1 / 2 of the original
The current should be squared
It's right that the current is high and the power is high
Remember it's a series circuit. Thank you. What about a parallel circuit? Parallel circuit is a lot of small circuits and do not affect each other, and the more electrical appliances in parallel, the smaller the resistance. The resistance formula of parallel circuit is: the reciprocal of the total resistance, etc
Series connection is a circuit with high resistance and low power
Because as the resistance increases, the current decreases,
For example, if the resistance is doubled, the current will be 1 / 2 of the original
If P = I2R is used, the electric power will be 1 / 2 of the original
The current should be squared
It's right that the current is high and the power is high
Remember it's a series circuit. Question: Thank you. What about the parallel circuit?
The area of a triangle is 30cm square. Find the functional relationship between the height y (CM) and the bottom x (CM) on the bottom, and make the image of this function
Images can't be drawn,
30=xy/2
So y = 60 / X
Inverse scale function
30=xy/2
So y = 15 / X
Inverse scale function.
In the known sequence an, the sum of the first n terms is Sn, A1 = 1, and an + 1 = 2Sn. Find the general term formula and Sn of an
Because: an + 1 = 2Sn, then a (n-1) + 1 = 2S (n-1)
Then: 2sn-2s (n-1) = (an + 1) - (a (n-1) + 1) (n > = 2)
And because: 2sn-2s (n-1) = 2An (n > = 2)
So: 2An = (an + 1) - (a (n-1) + 1)
An = - A (n-1) (n > = 2)
That is: an / a (n-1) = - 1, is an equal ratio sequence
So: an = (- 1) ^ (n-1) (n > = 2)
When n = 1, we can get A1 = 1, which is the same as the given condition, so it is also suitable for the formula: an = (- 1) ^ (n-1)
To sum up, an = (- 1) ^ (n-1)
By taking an into an + 1 = 2Sn, we get
Sn=[(-1)^(n-1)+1]/2
Because: an + 1 = 2Sn, then a (n-1) + 1 = 2S (n-1)
Then: 2sn-2s (n-1) = (an + 1) - (a (n-1) + 1) (n > = 2)
And because: 2sn-2s (n-1) = 2An (n > = 2)
So: 2An = (an + 1) - (a (n-1) + 1)
An = - A (n-1) (n > = 2)
That is: an / a (n-1) = - 1, equal ratio sequence = 2)
And because: 2sn-2s (n-1) = 2An (n > = 2)
So: 2An = (an + 1) - (a (n-1) + 1)
An = - A (n-1) (n > = 2)
That is: an / a (n-1) = - 1, is an equal ratio sequence
So: an = (- 1) ^ (n-1) (n > = 2)
When n = 1, we can get A1 = 1, which is the same as the given condition, so it is also suitable for the formula: an = (- 1) ^ (n-1)
To sum up, an = (- 1) ^ (n-1)
By taking an into an + 1 = 2Sn, we get
Sn = [(- 1) ^ (n-1) + 1] / 2