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Within 100, two-step calculation
I have 100 apples, Zhang San took some, Li Si took 32, and 35. How many did Zhang San take
I have 100 apples, Zhang San took part, Li Si took 33, and 35. How many apples did Zhang San take
There are 23 cars, 11 trucks and 65 vans in the parking lot. How many cars are there in the parking lot?
There are 96 candies in the kindergarten, including 32 in the big class and 37 in the small class. The rest are in the middle class. How many are in the middle class?
I have 12 watermelons, I ate five, gave five, how many more?
== Oh, second grade
There is a book with 100 pages. I read part of it today, 48 pages yesterday and 26 pages left. How many pages have I read today?
I have 10 pens. Xiaohong has two more pens than me, and Xiaoyun has three fewer pens than Xiaohong. How many pens does Xiao Yun have?
Let Sn be the sum of the first n terms of the arithmetic sequence {an}, and A1 = 7, S5 = 15
a2=a1+d
a3=a1+2d
.
s5=a1+a2+a3+a4+a5=5a1+d+2d+3d+4d=5a1+10d=15
If A1 = 7 is brought in, 5 * 7 + 10d = 15 can be obtained
The solution is d = - 2
If the first term is known and the tolerance is known, then the sequence will come out
Because the question does not ask for anything, there is no way to continue to answer
I don't believe you will
S5 = (a1 + A5) * 5 / 2 to get A5
Solving equations again
In fact, it's OK to solve A5 directly by using the sum of the first n terms
s5=5*7+[(5*4)/2}d=35+10d=15,==> 7+2d=3==>2d=-4==>d=-2
{an}=7-2（n-1）=7-2n+2= 9-2n
{sn}=7n+(-1)*n(n-1)=7n-n^2+n=-n^2+8n
Two units of electric work (J, kW. H) can j be said to be w
Yes, because work = power × time, J, W, s are SI units
Addition, subtraction, multiplication and division are expressed in words
1. The distance between Beijing and Shanghai is about 1000km. Assuming that sound can travel so far in the air, how long does it take for a train to travel from Beijing to Shanghai? How long does it take for a jumbo jet to travel from Beijing to Shanghai? Find the data you need and calculate it. (sound speed has been calculated at 340m / s)
2. Sound can propagate in the opposite direction when encountering obstacles. A student wants to shout at the bottom of a dry well. After 1.5 seconds, he hears the echo. How many meters is the depth of the ancient well? (the sound speed has been calculated as 340m / s)
If you can help me to say the following problem-solving ideas better
Sound travels at 340 / s in the air with a temperature of 15 ℃,
First of all, 1000 km should be converted into 1000000 M,
1000000 △ 340 is about 2941,
Turn 2941s into hours,
The final result is about 0.8 hours,
It takes about 0.8 hours from Beijing to Shanghai
(2) The speed of the train is 100km / s,
The distance is 1000km, 1000 △ 100 = 10, so it takes 10 hours for the train from Beijing to Shanghai
(3) The speed of a jumbo jet is 600km / h, the distance is 1000km, and 1000 △ 600 is about 1.67 hours, so it takes about 1.67 hours for a jumbo jet to travel from Beijing to Shanghai
2.340*1.5/2=255
Because the echo is reflected by the obstacle. After walking back and forth, it needs to be 2
Question 1: 340m / S = 20.4km/h, 1000km / 20.4km/h = 49.0196h
The average train speed is 140km / h, 1000km / 140km / h = 7.14h
The speed of jumbo jet is 800km / h, 1000km / 800km / h = 1.25h
Question 2: 340m / s times 1.. 5S divided by 2 = 255m
Sound travels at 340 / s in the air with a temperature of 15 ℃,
First of all, 1000 km should be converted into 1000000 M,
1000000 △ 340 is about 2941,
Turn 2941s into hours,
The final result is about 0.8 hours,
It takes about 0.8 hours from Beijing to Shanghai
(2) The speed of the train is 100km / s,
The distance is 1000km, 1000 ／ 100 = 10, so the train from Beijing to Shanghai needs 10
Sound travels at 340 / s in the air with a temperature of 15 ℃,
First of all, 1000 km should be converted into 1000000 M,
1000000 △ 340 is about 2941,
Turn 2941s into hours,
The final result is about 0.8 hours,
It takes about 0.8 hours from Beijing to Shanghai
(2) The speed of the train is 100km / s,
The distance is 1000km, 1000 △ 100 = 10, so it takes 10 hours for the train from Beijing to Shanghai
(3) The speed of a jumbo jet is 600km / h, the distance is 1000km, and 1000 △ 600 is about 1.67 hours, so it takes about 1.67 hours for a jumbo jet to travel from Beijing to Shanghai
2.340*1.5/2=255
Divide by 2 and put it away
In the known arithmetic sequence {an}, Sn is the sum of its first n terms, let A4 = - 2, S5 = - 20?
A4 = a1 + 3D = - 2 Formula One
s5=(a1+a4+d)*5/2=(a1-2+d)*5/2=-20
A1 + D = - 6 equation 2
Subtract two from one
2d=4
Substituting d = 2 into Formula Two
a1=-8
an=a1+(n-1)*d=-8+2n-2=2n-10
Physics ~ electric work and electric heating
W = uit, w = u squared T / R, w = I squared RT
What are the application scope of these three formulas?
What is neineng?
What is the conversion of electric energy into internal energy?
The physical meaning of the formula w = uit is that electric work is equal to voltage multiplied by current multiplied by on time, which is generally applicable
The square T / R of W = u and the square RT of W = I are suitable for pure resistance circuits (all electric energy is converted into heat energy)
In the non pure resistance circuit, the electric work w = uitand the electric heating q = the square RT of I
"Transforming electric energy into internal energy" refers to that after the conductor is electrified, the conductor will heat, the temperature will rise, the internal energy will increase, and the consumed electric energy will be transformed into the internal energy of the conductor
It is applicable to the amount of work done by electric energy on the resistance, where the resistance is pure resistance, that is, the converted energy is only internal energy, and does not include kinetic energy or other forms of energy
The internal energy is the sum of the kinetic potential energy of the molecules in the body. Macroscopic observation shows that the internal energy of the heated body is high
When the moving electrons (current) pass through the resistance, they do work on the resistance, that is, the current makes the molecules inside the resistance move more violently, and the internal energy is increased, which also consumes electric energy. ... unfold
It is applicable to the amount of work done by electric energy on the resistance, where the resistance is pure resistance, that is, the converted energy is only internal energy, and does not include kinetic energy or other forms of energy
The internal energy is the sum of the kinetic potential energy of the molecules in the body. Macroscopic observation shows that the internal energy of the heated body is high
When the moving electrons (current) pass through the resistance, they do work on the resistance, that is, the current makes the molecules inside the resistance move more violently, and the internal energy is increased, which also consumes electric energy. Put it away
Find 200 questions in the first volume of the third grade mathematics
Note that the sum of the first n terms of the arithmetic sequence {an} is Sn, A2 + A4 = 6, S4 = 10. (1) find the general term formula of the sequence {an}; (2) let BN = an · 2n (n ∈ n *), find the first n terms and TN of the sequence {BN}
(I) let the tolerance of the arithmetic sequence {an} be D, from A2 + A4 = 6, S4 = 10, we can get 2A1 + 4D = 64a1 + 4 × 32D = 10, (2 points), that is, a1 + 2D = 32a1 + 3D = 5, and the solution is A1 = 1D = 1, (4 points) ∧ an = a1 + (n-1) d = 1 + (n-1) = n, so the general formula of the arithmetic sequence {an} is an = n. (5 points) (II) according to the meaning of the problem, BN = an · 2n = n · 2n, ∧ TN = B1 + B2 + + BN = 1 × 2 + 2 × 22 + 3 × 23 + (n-1) (7 points) and 2tn = 1 × 22 + 2 × 23 + 3 × 24 + +The subtraction of (n-1) · 2n + n · 2n + 1, (9 points) results in - TN = (2 + 22 + 23 + + 2N-1 + 2n) - n · 2n + 1 (11 points) = 2 (1 − 2n) 1 − 2 − n · 2n + 1 = (1-N) · 2n + 1-2, (12 points) ｜ TN = (n-1) · 2n + 1 + 2. (13 points)
The following can not be regarded as the unit of electric work
A. Degree B. watt C. Joule D. kWh
B
The vertical problem of decimal addition, subtraction, multiplication and division in the fourth grade
Medium, 200
1.1.25+2.41 2.4.8-2.8 3.1.3+2.5 4.3.11+2.22 5.26.2-13.1 6.12.3+11.2 7.35.8-13.3 8.25.2+21.6 9.3.16+0.23 10.0.23+0.18 11.1.45+0.4 12.10.85-0.05 13.51.5-26.5 14.26.5+25 15.51.5-1.5 16.51.5+26.5 17.45.2-...
12.3+25.6 43.6+78.9 2.333333-1.222 52.31+5.36 13.51+52.39 21.36+78.41 12.369+41.852 78.21--12.36 13.56+52.36
RELATED INFORMATIONS
- 1. It is known that the sum of the first n terms of the arithmetic sequence {an} with tolerance greater than zero is Sn and satisfies a3a4 = 117, A2 + A5 = 22?
- 2. Is there any contradiction between electric work formula and electric heating formula Electric work formula: w = uit Electrothermal formula: q = I & # 178; RT For the pure resistance circuit, all the electric energy is converted into heat energy, w = Q For the non pure resistance circuit, part of the electric energy is converted into heat energy, w > Q According to Ohm's law, I = u / R, w = uit = u & # 178; t / R, q = I & # 178; RT = u & # 178; t / R, w = Q So how does w > Q come from? Is Ohm's law invalid for non pure resistance circuit?
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- 6. Xiaohong, Xiaohua and Xiaoli go to the bookstore together to buy the same book. If each person buys one book, Xiaohong's difference is 2.4 yuan, Xiaohua's difference is 4.5 yuan, and Xiaoli's difference is 0.5 yuan; If the sum of three people's money is just enough to buy two books, then one book is () yuan, and Xiao Li brings () yuan more than Xiao Hong?
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- 11. Unit conversion (pound, Newton, inch, centimeter) There is one category: it has a tear force standard of 57 pounds per inch Now the result of my measurement: 159 n / cm Excuse me: can I pass the standard test? Is it 57 lb / in or 159 n / cm? Copy the party, please respect yourself!
- 12. It is known that {an} is an arithmetic sequence, the sum of the first n terms is Sn, A4 = 2, S5 = 20. Let TN = | A1 | + | A2 | + +|An |, find TN
- 13. Will 12345 and addition, subtraction, multiplication and division each use once, equal to 22? According to the simplest elementary school algorithm
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- 18. The first n terms and Sn = a1 + A2 + a3 +... Of known sequence an +If an satisfies an + 2snsn-1 = 0 (n is greater than or equal to 2) A1 = 1 / 2, calculate an
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