What is the length of a circle

What is the length of a circle

Know the radius r of the circle
Perimeter = 2 × π × R
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Formula of arc length
It is known that AB is 1cm and BC is 2 cm.AB Vertical BC, find the arc length of AC

According to known, draw
The real length of AC = radius = 2.236cm
∠α=63.43 ∠β=58.28
Substituting into the arc length formula I = 0.01745 × R ×∠ β
=0.01745×2.236×58.28
The arc length of AC is about 2.27cm

Discount sales formula of mathematics in grade one of junior high school

Profit = selling price purchase price (cost)
Price = purchase price + profit
Purchase price = selling price profit
Profit rate = profit / purchase price (cost) × 100%
Profit = purchase price × profit rate
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Equation formula of one variable, complete, all kinds of commonly used, chasing, meeting, selling, etc
If you are the one!

First of all, the unknowns must be clear, it will not be difficult in the future. According to the conditions, and their own set of unknowns out of the equation, some problems need to use the unknowns several times, that is an empirical problem. Come on! I believe you can learn it well! These methods just play a transitional role, really learn the equation does not need

On the formula of educational savings
Sum of principal and interest =? = (1 + interest rate × number of periods) × principal, interest = principal × interest rate × number of periods, interest rate =?

Sum of principal and interest = principal + Interest = (1 + interest rate × number of periods) × principal, interest = principal × interest rate × number of periods, interest rate = interest ／ principal ／ number of periods

The formulas for solving the travel problem of the equation meet, in the same direction, in a ring

A meeting problem (straight line) a's distance + B's distance = total distance (distance); a's speed + B's speed = speed sum; meeting time × speed sum = meeting distance; meeting distance △ speed sum = meeting time; meeting distance △ meeting time = speed sum; * opposite: meeting time = distance

Formula of travel problem and so on
If you can, I would like to ask in the case of not knowing the meeting time, meeting place, distance and speed

Overtaking: speed difference × overtaking time = overtaking distance
Pursuit distance △ speed difference = pursuit time (in the same direction)
Speed difference = pursuit distance △ pursuit time
The distance a passes - the distance b passes = the distance in time
Encounter:
Encounter distance △ speed sum = encounter time
Speed and time of encounter = distance of encounter
Encounter distance △ encounter time = speed and time
Distance a takes + distance b takes = total distance

What are the formulas related to primary school itinerary problem and pursuit problem?

Basic concept: the problem of travel studies the motion of an object. It studies the relationship among speed, time and travel
Basic formula: distance = speed × time; distance △ time = speed; distance △ speed = time
Key problem: determine the position during the journey
Encounter problem: speed and X encounter time = encounter distance (please write other formulas)
Pursuit problem: pursuit time = distance difference △ speed difference (write other formulas)
Flow problem: downstream stroke = (ship speed + water speed) × downstream time, upstream stroke = (ship speed water speed) × upstream time
Forward speed = ship speed + water speed, backward speed = ship speed - water speed
Hydrostatic velocity = (downstream velocity + upstream velocity) × 2 water velocity = (downstream velocity - upstream velocity) × 2
Flow problem: the key is to determine the speed of the object, refer to the above formula
Bridge problem: the key is to determine the distance of the object, refer to the above formula
For reference only:
[formula of sum difference problem]
(sum + difference) △ 2 = larger number;
(sum difference) △ 2 = less decimal
[formula of sum multiple problem]
And (multiple + 1) = a multiple;
One multiple x multiple = another number,
Or sum - a multiple = another number
[formula of difference multiple problem]
Difference (multiple-1) = smaller decimal;
Smaller number × multiple = larger number,
Or smaller number + difference = larger number
[formula of average problem]
Total quantity △ total copies = average
[formula of general travel problem]
Average speed × time = distance;
Distance △ time = average speed;
Distance / average speed = time
[formula of reverse travel problem]
The problem of reverse travel can be divided into two kinds: meeting problem (two people start from two places and walk in opposite direction) and separation problem (two people walk in opposite direction)
(speed and) × encounter (departure) time = encounter (departure) distance;
Distance of encounter (departure) / (speed sum) = encounter (departure) time;
Distance of meeting (leaving) and time of meeting (leaving) = speed and distance
[formula of travel in the same direction]
Catch up (pull out) distance (speed difference) = catch up (pull out) time;
Catch up (pull away) distance △ catch up (pull away) time = speed difference;
(speed difference) × overtaking time = overtaking distance
[formula of train crossing bridge problem]
(bridge leader + train leader) △ speed = bridge crossing time;
(bridge leader + train leader) △ bridge crossing time = speed;
Speed × crossing time = the sum of bridge and vehicle length
[formula of sailing problem]
(1) general formula:
Static water speed (ship speed) + current speed (water speed) = downstream speed;
Ship speed water speed = upstream speed;
(downstream speed + upstream speed) △ 2 = ship speed;
(downstream velocity - upstream velocity) 2 = water velocity
(2) the formula of two ships sailing in opposite directions:
Ship a's downstream speed + ship B's upstream speed = ship a's still water speed + ship B's still water speed
(3) the formula of two ships sailing in the same direction:
The static water velocity of fore (AFT) ship - the static water velocity of fore (AFT) ship = the speed of narrowing (widening) the distance between two ships

What is the formula of the difference multiple problem?

Sum multiple problem sum (multiple-1) = decimal × multiple = large number (or sum decimal = large number) difference multiple problem difference (multiple-1) = decimal × multiple = large number (or decimal + difference = large number) travel problem distance = time × speed = distance △ time = distance △ speed encounter problem encounter distance = speed

The formula of difference multiple problem
Other formulas also need to be written more and comprehensively
Nobody knows?

I know that: 1 number of each copy × copies = total number △ number of each copy = total number △ copies = number of each copy 2 1 times × multiples = multiples △ 1 times = multiples △ multiples = 1 times 3 speed × time = distance △ speed = time distance △ time = speed 4 unit price × quantity = total price