It is known that {an} is an arithmetic sequence, its tolerance is - 2, and A7 is the middle term of the equal ratio of A3 and A9, Sn is the sum of the first n terms of {an}, n ∈ n *, then the value of S10 is___ .

It is known that {an} is an arithmetic sequence, its tolerance is - 2, and A7 is the middle term of the equal ratio of A3 and A9, Sn is the sum of the first n terms of {an}, n ∈ n *, then the value of S10 is___ .

∵ {an} is an arithmetic sequence, its tolerance d = - 2, and A7 is the middle term of the equal ratio of A3 and A9, ∵ (a1-12) 2 = (a1-4) (a1-16), the solution is A1 = 20, ∵ S10 = 10A1 + 10 × 92d = 110, so the answer is: 110
It is known that SN is the sum of the first n terms of the equal ratio sequence {an}, and S4, S10 and S7 form the equal difference sequence (1). Prove that A3, A9 and A6 form the equal difference sequence
(2) If the sum of the first term of ana1 = 1}
(1) If the common ratio = 1, Sn = Na1, 2 * S10 = S4 + S7 = 20a1 = 11A1, A1 = 0, rounding off (this step is best written, sometimes there is a solution)
If the common ratio is not 1, Sn = A1 (1-Q ^ n) / (1-Q), 2 * S10 = S4 + S7, we get 2 * (1-Q ^ 10) = 1-Q ^ 4 + 1-Q ^ 7, we get
2 * q ^ 6 = 1 + Q ^ 3, multiply both sides by A3 to get 2a9 = A3 + A6
(2) The common ratio of An3 is Q ^ 3 = - 1 / 2, s'n = 2 / 3 (1 - (- 1 / 2) ^ n)
If the tolerance D of the arithmetic sequence {an} is not equal to 0, and A5, A9 and A15 are equal ratio sequence, then the common ratio is______ .
According to the meaning of the question, we can know that (a1 + 8D) 2 = (a1 + 4D) (a1 + 14d), we can get 2a1d = 8d2, we can get 4D = A1, q = a9a5 = a1 + 8da1 + 4D = 32
The power supply voltage is constant, R2 = 6 Ω, R3 = 12 Ω. The slide P of sliding rheostat R1 slides to the middle point. When the switches S1, S2 and S3 are closed, the indication of ammeter a will change
）When switches S1, S2 and S3 are closed, R2 and R3 are connected in parallel by 1 / R parallel = 1 / R1 + 1 / r2: R parallel = 6 Ω × 12 Ω / 6 Ω + 12 Ω = 4 Ω, u = I Parallel R parallel = 3A × 4 Ω = 12V (2) when switches S1 are closed, S2 and S3 are open, R1 and R2 are connected in series, so R series = u / I series = 12V / 0.6A = 20 Ω, so R1 = (R series - R2) × 2 = (20 Ω -...)
No supply voltage???
Picture?
Is there a diagram, or how S1, S2, S3 are connected in the circuit
0.6A follow up: it's this
The Mathematical Olympiad questions of grade four in primary school △ + △ = □ + □ + □, □ + □ + □ = 0 + 00 + 00O, △ + □ + 00 + 00O = 400,
A system of linear equations with three variables
△+△=□+□+□ => △=3□/2
□+□+□=○+○+○+○ => 2○=3□/2
△+□+○+○=400
The first two formulas are substituted into three formulas to get 3 □ / 2 + □ + 3 □ / 2 = 400 = > □ = 100, which are respectively substituted into two formulas
△=3□/2=150
2○=3□/2=150 => ○=75
□=100
△=150
○=75
Oral arithmetic exercises of decimal multiplication
Who has
1.2（4x-0.5）
2. - 3 (1-6 / 1 x)
3.-x+（2x-2）-（3x+5）
4.3a's square + 2A's Square - (2a's square-2a) + (3a-a's Square)
（1）2（4x-0.5）
(2) - 3 (1-6 / 1 x)
（3）-x+（2x-2）-（3x+5）
(4) The square of 3A + the square of 2A - (the square of 2a-2a) + (the square of 3a-a)
4.8x-0.6
-3-half x
-2x-7
Square of 4A + 5A
Taking the three sides of RT △ ABC as the sides, the areas of semicircles made outwards are S1, S2, S3 respectively, and S1 = 4, S2 = 8, then the length of AB is?
The three sides are: L1, L2, L3
∵S1=4,S2=8
∴pi*l1^2/2=4 l1^2=8/pi l2^2=16/pi
AB ^ 2 = 24 / PI or AB ^ 2 = 8 / PI
Ψ AB = 2 √ (6 / PI) ≈ 2.7640 or AB = 2 √ (2 / PI) ≈ 1.5958
ABCD * 4 = DCBA find out the number of ABCD
ABCD=2178
Let's consider a, a times 4 doesn't have carry, so it can only be 1 or 2. If it's 1, D is 4, and D times 4 is not 1, so excluding, then a is 2 and D is 8
Look at B again, B times 4 can not carry, according to the above reasoning can get the answer
Who has the oral arithmetic of decimal multiplication in grade five of primary school, 10
（1）1.5 × 1.5 = 2.25
（2）9.4 × 9.7 = 91.81
（3）7.4 × 1.2 = 8.88
（4）3.9 × 9.8 = 38.22
（5）5.9 × 5.5 = 32.45
（6）1.8× 9.5 = 17.1
（7）6.9 × 1.4 = 9.66
（8）9.6 × 5.7 = 54.72
（9）9.2 × 8.2 = 75.44
（10）8.8 × 0.1 = 0.88
————Zhuozhou Pindao TKD grid
10*20=200
50*20=1000
15*30=450
12*50=600
90*80=7200
12*6=72
50*50=2500
4000*50=200000
50*30=150
80*50=4000
Write hard. The foundation of mathematics is very important, especially oral arithmetic. In later life, if you master mathematics, you can avoid many chances of being cheated. And like in the future when you test, if you have strong oral arithmetic ability, you will have more time to think about problems.
Let me give you another example. In the civil service examination, there is the subject of administrative ability, and there are many math problems. The reason why you can't finish the examination is that if you have passed the oral arithmetic, you can do more questions in more time. Isn't that more opportunities than others. Remember, this is the word of mouth
Write hard. The foundation of mathematics is very important, especially oral arithmetic. In later life, if you master mathematics, you can avoid many chances of being cheated. And like in the future when you test, if you have strong oral arithmetic ability, you will have more time to think about problems.
Let me give you another example. In the civil service examination, there is the subject of administrative ability, and there are many math problems. The reason why you can't finish the examination is that if you have passed the oral arithmetic, you can do more questions in more time. Isn't that more opportunities than others. Oral arithmetic is time. Remember this sentence and study hard. come on. Put it away
0.4×0.4=0.16
0.5×0.7=0.35
1.7×5.5=9.35
0.8×0.3=0.24
5.5×0.7=3.85
3.5×2.7=9.45
0.6×0.6=0.36
0.7×0.8=0.56
0.5×0.5=0.25
0.7×0.5=0.35
25 * 4 = 100 125 * 8 = 1000 25 * 8 = 200 125 * 4 = 500 0.1 times any number that is not zero, the result will be reduced by 10 times, 0.01 will be reduced by 100 times, 0.001 will be reduced by 1000 times, a few decimal places after the decimal point will have several zeros, and then add... To expand
25*4=100 125*8=1000 25*8=200 125*4=500 If 0.1 is multiplied by any number that is not zero, the result will be reduced by 10 times, if 0.01 is reduced by 100 times, if 0.001 is reduced by 1000 times, if there are several decimal places after the decimal point, there will be several zeros, and then add one, but it must be 0.1 or 0.01