The seventh grade of junior high school

The seventh grade of junior high school

This is someone else's answer, I don't know, right
All the math formulas for Grade Seven
Multiplication and factorization
a2-b2=(a+b)(a-b) a3+b3=(a+b)(a2-ab+b2) a3-b3=(a-b)(a2+ab+b2)
Trigonometric inequality
|a+b|≤|a|+|b| |a-b|≤|a|+|b| |a|≤b-b≤a≤b
|a-b|≥|a|-|b| -|a|≤a≤|a|
The solution of quadratic equation with one variable
-b+√(b2-4ac)/2a -b-b+√(b2-4ac)/2a
The relationship between root and coefficient
X1 + x2 = - B / a X1 * x2 = C / A
Discriminant b2-4a = 0 note: the equation has two equal real roots
B2-4ac > 0 note: the equation has a real root
b2-4ac0
Parabolic standard equation y2 = 2px y2 = - 2px x2 = 2PY x2 = - 2PY
Side area of straight prism s = C * h side area of oblique prism s = C '* h
Side area of pyramid s = 1 / 2C * h'side area of pyramid s = 1 / 2 (c + C ') H'
The area of the side of the cone s = 1 / 2 (c + C ') l = pi (R + R) l the surface area of the ball s = 4Pi * R2
Cylinder side area s = C * H = 2pi * h cone side area s = 1 / 2 * c * l = pi * r * l
The arc length formula L = a * r a is the arc number of the center angle R > 0 and the sector area formula s = 1 / 2 * L * r
Cone volume formula v = 1 / 3 * s * h cone volume formula v = 1 / 3 * pi * r2h
Volume of oblique prism v = s'L note: where s' is the area of straight section and l is the length of side edge
Cylinder volume formula v = s * h cylinder v = pi * r2h
The 0 at the end of each level is not read
Read 0 before each level
No matter how many zeros there are in the middle of each level, only one is read-only
A cone is one third of a cylinder
A cylinder is three times as big as a cone
If the numerator is the same, the smaller the denominator, the larger the fraction
With the same denominator, the larger the numerator, the smaller the fraction
The top is the numerator and the bottom is the denominator
Encounter problem
Encounter distance = speed and encounter time
Encounter time = encounter distance and speed
Speed sum = encounter distance encounter time
Profit and discount
Profit = selling price cost
Profit margin = profit cost 100% = (cost of sold price - 1) 100%
Amount of increase or decrease = percentage of increase or decrease of principal
Interest = principal interest rate time
After tax interest = principal interest rate time (1-20%)
Length Conversion
1 km = 1 000 m 1 m = 10 decimeters
1 decimeter = 10 cm 1 meter = 100 cm
1 cm = 10 mm
Area Conversion
1 sq km = 100 ha
1 ha = 10000 M2
1 square meter = 100 square decimeter
1 square decimeter = 100 square centimeter
1 sq cm = 100 sq mm
Volume (volume) product unit conversion
1 cubic meter = 1000 cubic decimeter
1 cubic decimeter = 1000 cubic centimeter
1 cubic decimeter = 1 liter
1 cc = 1 ml
1 cubic meter = 1000 liters
Conversion of weight unit
1 ton = 1000 kg
1kg = 1000g
1kg = 1kg
Conversion of RMB units
1 yuan = 10 Jiao
1 jiao = 10 points
1 yuan = 100 points
time conversion
1 century = 100 years 1 year = December
Big month (31 days): January, March, may, July, August, October, December
Small month (30 days): April, June, September and November
The average year is 28 days in February and leap year is 29 days in February
There are 365 days in a normal year and 366 days in a leap year
1 day = 24 hours, 1 hour = 60 minutes
1 minute = 60 seconds 1 hour = 3600 seconds
Number of copies × number of copies = total number △ number of copies = number of copies
Speed × time = distance △ speed = time
Distance △ time = speed unit price × quantity = total price
Total price / unit price = quantity total price / quantity = unit price
Work efficiency × work time = total amount of work △ work efficiency = total amount of work time △ work time = work efficiency Plus + Plus = sum
Sum - one addend = another addend minus - minus = difference
Subtracted difference = subtracted difference + subtracted = subtracted
Factor × factor = product △ one factor = another factor
Divisor / divisor = quotient divisor / quotient = divisor
Quotient x divisor = divisor
The problem of sum times
(sum + difference) △ 2 = large number (sum difference) △ 2 = decimal
Sum (multiple-1) = decimal × multiple = large number
Sum - decimal = large
Differential multiple problem
Difference (multiple-1) = decimal × multiple = large number
Decimal + difference = large number
Encounter problem
Encounter distance = velocity sum × encounter time encounter time = encounter distance △ velocity sum
Speed sum = encounter distance △ encounter time
Profit and discount
Profit = selling price cost profit rate = profit △ cost × 100% = (selling price △ cost-1) × 100%
Discount = actual selling price △ original selling price × 100% (discount ＜ 1) interest = principal × interest rate × time after tax interest = principal × interest rate × time × (1-20%)
Additive exchange rate: a + B = B + A
Addition binding rate: a + B + C = a + (B + C)

Mathematics formula and concept

The law of multiplication:
Commutative law of multiplication: a × B = B × a
Multiplicative Association Law: a × B × C = a × (B × C)
Multiplicative distribution law: a × C + B × C = C × (a + b)
a×c - b×c=c×(a - b)
Nature of division: a △ B △ C = a △ B × C
Subtraction property: a – B - C = a - (B + C)
Solving equation law:
Addend + addend = sum;
Addend = and - another addend
Subtraction - subtraction = difference;
Subtracted = difference + subtracted;
Subtraction = subtracted - difference
Factor × factor = product;
Factor = product △ another factor
The divisor is the quotient;
Divisor = quotient × divisor;
Divisor = divisor / quotient
Travel problems:
Distance = speed × time;
Time = distance △ speed;
Speed = distance △ time
Encounter problems:
Encounter distance = (a speed + B speed) × encounter time;
Encounter time = encounter distance (a speed + B speed);
The speed of a = the distance of meeting △ the time of meeting - the speed of B;
Speed B = distance to meet △ time to meet - speed a
Engineering problems
Total amount of work = work efficiency × work time;
Working time = total amount of work △ working efficiency;
Work efficiency = total amount of work △ working time;
Total amount of work = planned work efficiency × planned work time;
Total amount of work = actual work efficiency × actual working time;
Actual working time = total amount of work △ actual working efficiency;
Actual work efficiency = total amount of work △ actual working time;
Buying and selling problems:
Total amount = unit price × quantity;
Quantity = total amount △ unit price;
Unit price = total amount △ quantity
Grade 6
(1) S = nr2-nr2 or S = n (r2-r2)
(2) (a-b) divided by B * 100% or (B-A) divided by B * 100%
(3) Attendance divided by total attendance
(4) B * (1 + C%) or b * (1-C%)
(5) Interest = principal * interest rate * time, interest tax = principal * interest rate * time * (1-5%)
(6) A divided by (1 + C%) or a divided by (1-C%)
Grade 7
Common mathematical formula table: formula expression
Square difference A2-B2 = (a + b) (a-b)
The square of sum and difference (a + b) 2 = A2 + B2 + 2Ab (a-b) 2 = A2 + b2-2ab
The cube of sum and difference A3 + B3 = (a + b) (A2 AB + B2) a3-b3 = (a-b) (A2 + AB + B2)
Trigonometric inequality | a + B | ≤| a | + | B | A-B | ≤| a | + | B | a | ≤ B-B ≤ a ≤ B
|a-b|≥|a|-|b| -|a|≤a≤|a|
Solutions of quadratic equation of one variable - B + √ (b2-4ac) / 2A - B-B + √ (b2-4ac) / 2A
The relation between root and coefficient X1 + x2 = - B / a X1 * x2 = C / A
Discriminant b2-4a = 0 note: the equation has two equal real roots
B2-4ac > 0 note: the equation has a real root
b2-4ac0
Parabolic standard equation y2 = 2px y2 = - 2px x2 = 2PY x2 = - 2PY
Common mathematical formula table: geometric formula
Side area of straight prism s = C * h side area of oblique prism s = C '* h
Side area of pyramid s = 1 / 2C * h'side area of pyramid s = 1 / 2 (c + C ') H'
The area of the side of the cone s = 1 / 2 (c + C ') l = pi (R + R) l the surface area of the ball s = 4Pi * R2
Cylinder side area s = C * H = 2pi * h cone side area s = 1 / 2 * c * l = pi * r * l
Arc length formula L = a * r (a is the arc number of the center angle R > 0) sector area formula s = 1 / 2 * L * r
Cone volume formula v = 1 / 3 * s * h cone volume formula v = 1 / 3 * pi * r2h
Cylinder volume formula v = s * h cylinder v = pi * r2h
Volume of oblique prism v = s'L (s' is the area of straight section, l is the length of side edge) Note: pi = 3.14159265358979

All the formulas of Mathematics

The law of multiplication: the commutative law of multiplication: a × B = B × a, the associative law of multiplication: a × B × C = a × (B × C) the distributive law of multiplication: a × C + B × C = C × (a + b) a × C - B × C = C × (a - b)} the nature of division: a △ B △ C = a × (B × C)} the nature of subtraction: a – B - C = a - (B + C)} the solution

You'd better ask another question,

Encounter problem
Encounter distance = speed and X encounter time
Encounter time = encounter distance △ speed and
Speed sum = encounter distance △ encounter time
Follow up questions
Pursuit distance = speed difference × pursuit time
Pursuit time = pursuit distance △ speed difference
Speed difference = pursuit distance △ pursuit time
A team is 450 meters long and advances at a speed of 90 meters per minute. After someone takes something from the end of the line to the head of the line, he immediately returns to the end of the line at a speed of 3 meters per second?
Comment: this problem is actually divided into two processes: ① the process from the end of the line to the head of the line is a process of catching up, which is equivalent to the last person catching up with the person in front; ② the process from the head of the line to the end of the line is a process of meeting, which is equivalent to walking from the head of the line to meeting the person at the end of the line
In the process of catching up, if the time of catching up is x seconds and the speed of the team is 90 m / min = 1.5 m / s, the distance of the first line is 1.5 x meters; if the speed of the pursuer is 3 M / s, the distance of the pursuer is 3x meters
3x－1.5x=450 ∴x=300
In the process of meeting, let the time of meeting be y seconds, and the speed of the team and the returnees remain unchanged. Therefore, the distance of the tail runner is 1.5y meters, and the distance of the returnees is 3Y meters. According to the equal relationship in the meeting problem, "the distance of a + the distance of B = the total distance" is: 3Y + 1.5y = 450  y = 100
So the total round trip time is x + y = 300 + 100 = 400 (seconds)

Is there a formula for seventh grade math clock problem? If so, please say it

A basic formula is as follows: the number of squares to catch up at the initial time △ (1-1 / 12) = the time to catch up (minutes), where 1-1 / 12 is the number of squares that the minute hand moves more than the hour hand per minute. The minute hand can walk 6 degrees in a minute, and the hour hand can walk 0.5 degrees

1. Evaluation
（1）1-tan15°/1+tan15°
（2）1+tan75°/1-tan75°

1-tan15°/1+tan15°
=tan45°-tan15°/1+tan45°*tan15°
=tan(45-15)°
=√3/3
Similarly = - √ 3

Math formula in Grade Seven

Multiplication and factorization
a2-b2=(a+b)(a-b) a3+b3=(a+b)(a2-ab+b2) a3-b3=(a-b)(a2+ab+b2)
Trigonometric inequality
|a+b|≤|a|+|b| |a-b|≤|a|+|b| |a|≤b-b≤a≤b
|a-b|≥|a|-|b| -|a|≤a≤|a|
The solution of quadratic equation with one variable
-b+√(b2-4ac)/2a -b-b+√(b2-4ac)/2a
The relationship between root and coefficient
X1 + x2 = - B / a X1 * x2 = C / A
Discriminant b2-4a = 0 note: the equation has two equal real roots
B2-4ac > 0 note: the equation has a real root
b2-4ac0
Parabolic standard equation y2 = 2px y2 = - 2px x2 = 2PY x2 = - 2PY
Side area of straight prism s = C * h side area of oblique prism s = C '* h
Side area of pyramid s = 1 / 2C * h'side area of pyramid s = 1 / 2 (c + C ') H'
The area of the side of the cone s = 1 / 2 (c + C ') l = pi (R + R) l the surface area of the ball s = 4Pi * R2
Cylinder side area s = C * H = 2pi * h cone side area s = 1 / 2 * c * l = pi * r * l
The arc length formula L = a * r a is the arc number of the center angle R > 0 and the sector area formula s = 1 / 2 * L * r
Cone volume formula v = 1 / 3 * s * h cone volume formula v = 1 / 3 * pi * r2h
Volume of oblique prism v = s'L note: where s' is the area of straight section and l is the length of side edge
Cylinder volume formula v = s * h cylinder v = pi * r2h
The 0 at the end of each level is not read
Read 0 before each level
No matter how many zeros there are in the middle of each level, only one is read-only
A cone is one third of a cylinder
A cylinder is three times as big as a cone
If the numerator is the same, the smaller the denominator, the larger the fraction
With the same denominator, the larger the numerator, the smaller the fraction
The top is the numerator and the bottom is the denominator
Encounter problem
Encounter distance = speed and encounter time