Why is pi used in finding the area of a circle?
482997
because the definition of pi is the ratio of a circle's circumference to its diameter, or \n\npi = circumfrance:diameter\n\nthis ratio always equals 3.14.... , it's a constant
129445
Pi is the ratio of the circumferance of a circle to its diameter.  The following equation is for the area of a circle:    A = pi*r^2\n\nThe Math Forum website has a very complete and east-to-understand explanation.
1019391
Area is the measure of the two-dimensional size of any shape. Area is calculated in different ways for different shapes, for example, for a rectangle A = l x h (length multiplied by height), for a triangle A = 1/2 b x h (half of the base multiplied by the height), and for a circle A = pie x r^2 (pie multiplied by the square of the radius).\n\nPerimeter is simply the distance around a figure, or the total length of the border of a shape. Again, perimeter is calculated in different ways for different shapes. For a rectangle, P = 2 (l + h) and for a circle the perimeter is called the 'circumference', nd calculated by the formula C = 2 x pie x r.
1120961
Simply put, a string can be used to go around the circle. Mark where the first end meets the other then measure on a ruler. Record that. Then u measure the diameter ( the line that parts in two equal parts). Divide the diameter into the circumference and u r supposed to get 3.14 or close to that which is pi. So pi is the ratio of the diameter to circumference. Simply put!!!
78720
Pi is a name given to the ratio of the circumference of a circle to the diameter. That means, for any circle, you can divide the circumference (the distance around the circle) by the diameter and always get exactly the same number. It doesn't matter how big or small the circle is, Pi remains the same. Pi is often written using the symbol  and is pronounced "pie", just like the dessert.
569561
Pi is the ratio of circumference to diameter. The Indians, the Egyptians, the Greeks and the Babylonians all knew that the ratio of the circumference to the diameter of a circle is the same for all circles, and that it is slightly more than 3. The Indians and Greeks also knew that the area of a circle is πr^2. Archimedes showed that the volume of a sphere is (4/3)πr^3 and that the surface area of a sphere is 4πr^2. By finding perimeters of circumscribed and inscribed regular polygons, Archimedes found that π is between 3 + 10/71 and 3 + 1/7.  In 1761, Johann Heinrich Lambert showed that π is an irrational number by showing that it has a generalized continued fraction that does not terminate. In 1882, Ferdinand von Lindemann proved that π is a transcendental number. With the appearance of computers, a hunt on millions and billions of decimal places of π has started and is still ongoing.
820614
So am I answering a homework question for you? lol\n\nCircles have the minimal perimeter for the area contained.\nArea of a circle is pi x Radius x Radius. (pi R squared)\n\nNext best would be something close to a circle, so consider a hexagon or octagon, with the corners of the square intersecting the vertices of the outer figure.\n\nLet's try a circle first...\n\nDiameter of the circle would be the diagonal of the square, or five times the square root of two.  5 x 1.414 = 7.07.  So the Radius is 3.535 meters.\n\nPi x 3.535 x 3.535 = 3.14 x 12.5 = 39.34\n\nSo the circle solution is too big.\n\nNow work out on paper what an octagon or hexagon surrounding the square would look like.  One of those should be about 34 m square.  Remember the area of the square is already 25 m2, so you are looking for only 9 more m2.\n\nI played around for minute or so in paint, and came up with a parallelogram that worked too.  Finally, a smooth curving perimeter shape get you benefits similar to the "circle" solution, so an ellipse would be a good comparison solution.  Try that, and compare the perimeter result against the perimeter of the parallelogram, which has a perimeter of 24.23 meters.\n\nHave fun!\nOC
280930
I don't know this equation, but pi is the greek letter P. it can be used for any variable, but since it is widely accepted as the constant 3.1415 (= a circles circumference divided by its diameter) this would be a dumb decision.\n\nFor example when you need to sum many values, you use the Sigma, but for multiplying many values you use the big PI.\n\ngrtz,\nGB
492563
This cannot be the whole question.  Since you are using the letters r and d, I will assume you are talking about radius and diameter.\nAre you trying to find the area? then use the formula\nA = Pi*r^2\nIf you are trying to find circumference, then use\nC = 2*Pi*r\nRemember that d = 2r (diameter is twice the radius)
426495
It depends on what shape you want to know the area.\n\nSimple shapes have formulas. (such as a circle's area is Pi*r*r)\n\nComplex shapes which have pattern.(you know the equation of lines that form the shape), calculus is used to find the area.\n\nIf a shape is not ordinary. You should draw lines to grid it and count the area square by square.\n\n-Hope this would help-
325893
PI= π = 22/7 = 3.1428571428571428571428571428571\n\nIn Euclidean plane geometry, π may be defined either as the ratio of a circle's circumference to its diameter, or as the ratio of a circle's area to the area of a square whose side is the radius. Advanced textbooks define π analytically using trigonometric functions, for example as the smallest positive x for which sin(x) = 0, or as twice the smallest positive x for which cos(x) = 0.\n\nAll these definitions are equivalent, they amount to the following numerical value of π, truncated to 50 decimal places:\n\n3.14159 26535 89793 23846 26433 83279 50288 41971 69399 37510
729233
limit is not specified so we asume whole area\n\nx^2+y^2 = a^2\n\nthis is a circle of radius a\n\nso area = pi*a^2
601593
Circumference is the distance around a circle.  2 times pi ( which is about 3.14) times the radius (the distance from the center of the cirle to any side).  In formula form it looks like this C = 2*Pi*r.\n\nThe formula for area of a circle is A = Pi*r^2 ( also known as r squared)
310080
Area = pi times radius squared, so divide the diameter by 2 and go from there
884700
An entire circle has 2pi radians.  You just want pi/3 radians.  What part of 2 is 1/3?  In other words, what do you have to multiply pi/3 by to get 2pi.  (psst: it's 6).  So you want 1/6 of the circle's area.\n\npi/3 is an angle worth remembering.  The cosine of it is 1/2.
461233
In Euclidean plane geometry, π may be defined either as the ratio of a circle's circumference to its diameter, or as the ratio of a circle's area to the area of a square whose side is the radius. Advanced textbooks define π analytically using trigonometric functions, for example as the smallest positive x for which sin(x) = 0, or as twice the smallest positive x for which cos(x) = 0.\n\nAll these definitions are equivalent, they amount to the following numerical value of π, truncated to 50 decimal places:\n\n3.14159265358979323846264338327950288419716939937510
1159698
I am a math teacher who just finished teaching how to find the area of circle involving pi. The students were greatly interested in the concept of pi. For you to memorize the first 1018 digits of pi is highly impressive. To do it in 5 minutes is nothing short of astounding. You should be extremely proud. Congratulations!