In the experiment of measuring resistance by volt ampere method, when measuring constant value resistance, we can find the average value of resistance by measuring multiple groups of voltage and current values. But when measuring the resistance value of small bulb, we can't find the average value many times. Why?

This is because the bulb generates heat when it emits light with the passage of current, and the resistance will increase with the increase of temperature, so it is impossible to measure the average value for many times

Factorization of (AB-1) ^ 2 + (a + b-2) (a + b-2ab) by substitution

From December 6, 2009 to May 29, 2012. How many days in total?

3 × 365 + 25 + 31 + 29 + 31 + 30 + 29 = 1270 days

The total age of the three members of Li Xiaodong's family is 86 years old. His father is three years older than his mother. 12 years ago, the total age of the whole family was 51 years old. How old is his father? How old is his mother? How old is he?
2. The age of a is four years younger than that of B, which is three times as old as that of B. the age of a was the same as that of B seven years ago and that of B nine years later?
3. Father and son are 69 years old now. 12 years ago, father's age is four times that of son's. Q: how old are father and son now?
You can't use X or Y!

3. Father and son are 69 years old now. 12 years ago, father's age is four times that of son's. Q: how old are father and son now?
69-12 * 2 = 45 years old
45 / (4 + 1) = 9 (years old)
9 + 12 = 21 years old
9 * 4 + 12 = 48 years old
A: father's age is 48, son's age is 21
The total age of the three members of Li Xiaodong's family is 86 years old. His father is three years older than his mother. 12 years ago, the total age of the whole family was 51 years old. How old is his father? How old is his mother? How old is he?
86-12 * 3 = 50 years old
50 years old

At the end of each year, the deposit is 1000 yuan, with a term of 10 years, an annual interest rate of 12%, and compound interest once every half a year?
The process!

1、 Compound interest
Deposit cycle once a year, 10 years is 10 times
Annual interest rate is 12%, compound interest once a half year, compound interest twice a year
Get: cycle rate = (1 + 12% / 2) ^ 2-1 = 12.36%
Apply the final value of annuity to get the sum of capital and interest at the end of 10 years
That is, the sum of capital and interest at the end of 10 years = 1000 * ((1 + 12.36%) ^ 10-1) / 12.36% = 17857.08 yuan
2、 Simple interest
Deposit once a year, 10 years is 10 times
It can be seen that the deposit at the end of the first year has 9-year interest, and the deposit at the end of the tenth year has no interest
In other words, the sum of capital and interest at the end of 10 years = 1000 * (1 + 12% * 9) + 1000 * (1 + 12% * 8) +... + 1000 = 1000 * 9 * (1 + 12% * (1 + 9) / 2) + 1000 = 15400 yuan
The above answers, I hope to help you

Who can help me summarize all the key formulas of junior high school mathematics
Junior high school forget a lot, no time to make up, can't finish 6 books, just focus on the 'algebraic function = = what formula to Oh``

The purpose of multiplication and multiplication is to get the result of the multiplication and the multiplication and the multiplication and the multiplication and the multiplication is the result of the formula A2-B2 = (a + b) (a-b) (a2-ab + B2) a3-b3 = (a + b) (a2-ab + B2) (a-b (a-b (A2 + AB + B2) triangle inequality (a-b (a-b (a-b (A2 + AB + A2 + AB + B2)) triangle inequality |a (a + B |a + B 124\\124\|a (a 124\\124\\124124\\\\\\124a | solutions of quadratic equation of one variable - B + √ (b2-4ac) / 2A - B - √ (B2 -...)

1 / 5 times 3.7 + 6.3 times 1 / 5 + 4.4, how to calculate

1 / 5 times 3.7 + 6.3 times 1 / 5 + 4.4,
=1/5×（3.7+6.3）+4.4
=2+4.4
=6.4

A clothing factory is going to process 400 sets of sportswear. After 160 sets of sportswear are processed, new technology is adopted to improve the work efficiency by 20% compared with the original plan. As a result, it takes 18 days to complete the task. How many sets of sportswear are processed in the original plan?

Suppose that the original plan is to process x sets per day, from the meaning of the question: 160x + 400 − 160 (1 + 20%) x = 18. The solution is: x = 20. It is tested that x = 20 is the solution of the original equation. Answer: the original plan is to process 20 sets per day

Calculate 0.1 * 0.2 * 0.9 + 0.2 * 0.6 * 1.8 + 0.3 * 0.9 * 2.7 divided by 0.1 * 0.2 * 0.4 + 0.2 * 0.4 * 0.8 + 0.3 * 0.6 * 1.2

1 * 0.2 * 0.9 + 0.2 * 0.4 * 1.8 + 0.3 * 0.6 * 2.7 divided by 0.1 * 0.2 * 0.4 + 0.2 * 0.4 * 0.8 + 0.3 * 0.6 * 1.2 = 1 * 2 * 9 + 2 * 4 * 18 + 3 * 6 * 27 divided by 1 * 2 * 4 + 2 * 4 * 8 + 3 * 6 * 12 = 1 * 2 * 9 + 1 * 2 * 9 * 2 * 2 + 1 * 2 * 2 * 2 + 1 * 2 * 4 * 3 * 3 = 1 * 2 * 9 (1 + 8 + 27) divided by 1 * 2

All formulas of primary school mathematics

1. Each copy × copies = total number, total number / copies = copies, total number / copies = copies
2. Multiple 1 × multiple = multiple, multiple △ 1 = multiple, multiple △ 1 = multiple
3 speed × time = distance, distance △ speed = time, distance △ time = speed
4 unit price × quantity = total price, total price / unit price = quantity, total price / quantity = unit price
5. Working efficiency × working time = total amount of work, total amount of work △ working efficiency = working time / total amount of work △ working time = working efficiency
6 addends + addends = sum, and - one addend = another addend
7 subtraction subtraction = difference, subtraction difference = subtraction, difference + subtraction = subtraction
8 factor × factor = product, product △ one factor = another factor
9 divisor / divisor = quotient, divisor / quotient = divisor, quotient × divisor = divisor
Primary school mathematics figure calculation formula
1 square: C perimeter s area a side length, perimeter = side length × 4, C = 4A, area = side length × side length s = a × a
2. Cube: V: volume, a: edge length, surface area = edge length × edge length × 6, s surface = a × a × 6, volume = edge length × edge length × edge length, v = a × a × a
3 rectangle: C perimeter s area a side length, perimeter = (length + width) × 2, C = 2 (a + b), area = length × width, s = ab
4 cuboid: V: Volume s: Area A: length B: width H: height, (1) surface area (L × W + L × H + W × h) × 2, s = 2 (AB + ah + BH), (2) volume = l × w × h, v = ABH
5 triangle: s area a bottom h height, area = bottom × height △ 2
S = ah ／ 2, triangle height = area × 2 ／ bottom, triangle bottom = area × 2 ／ height
Parallelogram: s area a bottom h height, area = bottom × height, s = ah
7 trapezoid: s area a upper bottom B lower bottom h high, area = (upper bottom + lower bottom) × height △ 2, s = (a + b) × h △ 2
8 circle: s area C perimeter Π d = diameter r = radius, (1) perimeter = diameter ×Π = 2 ×Πx radius, C = Πd = 2 Π R, (2) area = radius × radius ×Π
9 cylinder: V: Volume H: height s; bottom area R: bottom radius C: bottom perimeter, (1) side area = bottom perimeter × height, (2) surface area = side area + bottom area × 2, (3) volume = bottom area × height, (4) volume = side area △ 2 × radius
10 cone V: Volume H: height s; bottom area R: bottom radius volume = bottom area × height △ 3 total number △ total number of parts = average number
The formula of sum and difference problem: (sum + difference) △ 2 = large number, (sum difference) △ 2 = decimal and multiple problem, sum (multiple-1) = decimal, decimal × multiple = large number, (or sum decimal = large number), difference multiple problem, difference (multiple-1) = decimal, decimal × multiple = large number (or decimal + difference = large number)
Tree planting problem: 1. The tree planting problem on non closed lines can be divided into the following three cases
(1) if trees are to be planted at both ends of the non closed line, then: number of trees = number of sections + 1 = total length ／ spacing-1, total length = spacing × (number of trees-1), spacing = total length ／ (number of trees-1)
(2) if trees are to be planted at one end of the non closed line and not at the other end, then: number of trees = number of sections = total length △ spacing, total length = spacing × number of trees, spacing = total length △ number of trees
(3) if trees are not planted at both ends of the non closed line, then: number of trees = number of sections - 1 = total length ／ spacing - 1, total length = spacing × (number of trees + 1), spacing = total length ／ (number of trees + 1)
2. The quantitative relationship of tree planting on closed lines is as follows: number of trees = number of segments = total length △ spacing, total length = spacing × number of trees, spacing = total length △ number of trees
Profit and loss: (profit + loss) △ the difference between the two distributions = the number of shares participating in the distribution
(big profit - small profit) △ the difference between the two distributions = the number of shares participating in the distribution
(big loss - small loss) △ the difference between the two distributions = the number of shares participating in the distribution
Encounter problem: encounter distance = velocity sum × encounter time, encounter time = encounter distance △ velocity sum, velocity sum = encounter distance △ encounter time
Chase problem: Chase distance = speed difference × chase time, chase time = chase distance ／ speed difference, speed difference = chase distance ／ chase time
Flow problems: downstream velocity = hydrostatic velocity + flow velocity, countercurrent velocity = hydrostatic velocity - flow velocity, hydrostatic velocity = (downstream velocity + countercurrent velocity) / - 2, flow velocity = (downstream velocity - countercurrent velocity) / - 2
Concentration problem: weight of solute + weight of solvent = weight of solution, weight of solute / weight of solution × 100% = concentration, weight of solution × concentration = weight of solute, weight of solute / concentration = weight of solution
The problem of profit and discount: Profit = selling price cost, profit rate = profit / cost × 100% = (selling price / cost-1) × 100%, up and down amount = principal × up and down percentage
Discount = actual selling price △ original selling price × 100% (discount ＜ 1), interest = principal × interest rate × time, after tax interest = principal × interest rate × time × (1-5%)