how do you find the center of a circle?
355170
with a compass!  or a ruler!
901448
Here's how to solve the problem:\n\nFirst find the center of the circle (call it (x1,y1).\n1. Write an expression for the distance of (x1,y1) from the first point, (1,8):  (x1-1)^2 + (y1-8)^2\n\n2. Write an expression for the distance of (x1,y1) from the second point, (-2,-1). (You should know how to do this, especially after seeing the example above.)\n\n3. Write an expression for the distance of (x1,y1) from the given line. This is a little trickier. There are probably various ways of approaching it. Here's one:\n\nRewrite the equation in slope-intercept form: y = (3/4)x +4\nThis tells us that the slope of the line is 3/4. So the slope of a line perpendicular to this line is -4/3. (The product of the two slopes has to be -1.)\n\nThe distance from (x1,y1) to the original line is measured along the direction perpendicular to that line. So it will be measured along a line with a slope of -4/3. The general equation for such a line is \ny = -(4/3)x + b, where b is the y-intercept of the line.\n\nNow we're trying to find an expression for the distance from (x1,y1) to the original line. To do this, we have to find where the perpendicular line intersects the original line. So we need to find the solution of the two equations, \ny = (3/4)x +4 and y = -(4/3)x + b.\nThis gives us two expressions for y, so we can set them equal:\n(3/4)x +4 = -(4/3)x + b\nSolving this, x = (12/25)(b-4) = (12b-48)/25\nAnd y = 9/25(b-4) + 4 = (9b +64)/25\nSo the point of intersection of the given line and the perpendicular line is ((12b-48)/25,(9b +64)/25).\n\nThe distance from (x1,y1) to this point (and to the given line) is \nsqrt((x1-(12b-48/25))^2 + (y1-(9b+64)/25)^2).\n\nHow do we find b and x1 and y1? We need to equate the three expressions for distance (this one, and the two found in items 1 and 2 above). Solving these equations will give us the center of the circle and the equation for the perpendicular to the given line.\n\nNext find the radius of the circle:\nDetermine the distance from the center to either of the two given points (using the Pythagorean theorem ... that is, using the distance formula). Call this distance D.\n\nFinally, write the equation of the circle:\n(x-x1)^2 + (y-y1)^2 = D^2
608708
The basic formula for a circle is (x-h)^2 + (y-k)^2 = r^2\n\n(h,k) would be the center (where x=h and where y=k), and the radius is the positive square root of r^2\n\nSo in your example, there is no h or k, so the center would be (0,0) and the radius would be the positive square root of 25, which is 5.
525762
(m)\n\nBY  FOUR-CENTER  METHOD The   four-center   method   is   used   for   small ellipses.  Given  major  axis,  AB,  and  minor  axis, CD, mutually perpendicular at their midpoint, O, as shown in figure 4-45, draw AD, connecting the end points of the two axes. With the dividers set to  DO,  measure  DO  along  AO  and  reset  the dividers on the remaining distance to O. With the difference  of  semiaxes  thus  set  on  the  dividers, mark  off  DE  equal  to  AO  minus  DO.  Draw perpendicular  bisector  AE,  and  extend  it  to intersect the major axis at K and the minor axis extended  at  H.  With  the  dividers,  mark  off  OM equal  to  OK,  and  OL  equal  to  OH.  With  H  as a  center  and  radius  R1 equal  to  HD,  draw  the bottom  arc.  With  L  as  a  center  and  the  same radius as R1, draw the top arc. With M as a center and the radius R2 equal to MB draw the end arc. With K as a center and the same radius, R2, draw the  end  arc.  The  four  circular  arcs  thus  drawn meet,  in  common  points  of  tangency,  P,  at  the ends  of  their  radii  in  their  lines  of  centers
276680
Ok, If A is a point on the circle and C is the middle of the circle then AC is the RADIUS of the circle.  Which means any point on the circle to C WILL ALWAYS be 12.  So if the excess of the circle to B is 8, then Add the RADIUS to the distance to B, and we arrive at the result of 20. Which is AC + (Distance of circle to B)\n\n20
1095202
The equation of a circle is:\n(x-h)^2 + (y-k)^2 = r^2\nwhere:\nh: x-coordinate of the center\nk: y-coordinate of the center\nr: Radius of the circle\n\nThe center of the circle will be midway between the points. On the x-axis:\n\n(-4 + 8)/2 = 4/2 = 2\n\nOn the y-axis:\n\n(2+8)/2 = 10/2 = 5\n\nSo the location of the center as coordinates is (2,5)\nThe radius is simply the distance from the center to either point. So, using the pathegreom theorm and the center at (h,k) and the point at (Px,Py):\n\nsqrt((h-Px)^2 + (k-Py)^2) = r\n\nUsing (8,8) for the point and the center at (2,5):\n\nsqrt((2-8)^2 + (5-8)^2) = sqrt((-6)^2 + (-3)^2) = sqrt(36 + 9) = sqrt(45)\n\nObviously, you could plug square root of 45 into your calculator to get some decimal equivilent, but it's not necessary since the equation requires r^2 anyways. So our final equation, using the form above, is:\n\n(x-2)^2 + (y-5)^2 = (sqrt(45))^2\n\nSimplifying, the square root and ^2 cancel out leaving:\n\n(x-2)^2 + (y-5)^2 = 45
595970
draw a line maesuring 2.5 cm..this is bc.then using a protractor make an angle of 60 degrees n on the angle measure the other side of 3.5 cm.join the end points and u get ur triangle.The circuncircle is a circle that touches all 3 vertices.then draw the perpendicular bisector of any two sides..the intersectin point becomes ur centre for the circle.now with the radius equal to the distance between the centre n the vertex draw a circle..tada!
401455
Sorry.  This is going to be a little rough, typing the answer.  Here it goes:  \n(x-2)2(squared)+ (y-4)2 (squared)= 25\n\nYou find the midpoint between the two points for the center.  You find the distance between the two points for the diameter and divide that in half for the radius which equals 5.  The center is (2,4).  You square the radius and that is what comes after the equals sign.\n\nThe guy who entered before me is wrong.  I promise.
226433
The circle's center is at (4, -1).  Therefore its radius is sqrt((6-4)^2 + (3- -1)^2) or sqrt 20.\n\nSo its equation is (x-4)^2 + (y+1)^2 = 20\n\nThe reason we know the center is at (4, -1) [at least how I did it] is by calling the center (a,b) and writing three different but equal applications of the distance formula, one from each known point to (a,b), then taking two pairs of these three distances, making them equal, and solving for a and b.
312528
The radius of a circle is the distance from the center of the circle to the edge of the circle.
50370
Draw a circle.  From the centre point to the edge draw a straight line.  This is the radius.  The area of a circle is pi times (radius squared.)  The Perimetre of a circle is 2 times pi times radius.
269071
Okay, what you want to do is find the circumference of the circle. That's 2(pi)r. That's 37.69911184... . Next find 32 as a decimal of this number - 32/(true cicumference). The fractional decimal is 0.8488263632... . Finally take this percentage and multiply it by 360 and you get 305.5774907... degrees or 305 degrees (accurate to 3 s.f.)
203653
http://en.wikipedia.org/wiki/Squaring_the_circle\n\nAll you need is there...
343495
To find arc length, you need the angle that the arc subtends and the radius of the circle.  To find the angle, you'd have to do some geometry...\n\nImagine a triangle with sides 10, 10, and 5.  This is pretty much a chord on your circle (5) and the radii from the center to the ends of the chord (10).  If you draw a line from the center perpendicular to the chord, it bisects the chord.  This gives you two right triangles, with hypotenuse 10, side 2.5 (half the chord), and side unknown (the segment from the center to the chord).  To find the angle at the center formed by the radius and the unknown, you can use the sine function:\n\nangle = arcsin(opposite/hypotenuse)\nangle = arcsin(2.5/10)\nangle = 14.48 degrees or 0.25 radians\n\nThe total angle is then 0.5 radians, since the above only found half of that total angle.\n\nThe formula for arc length is\n\narc length = radius * angle\n= 10 cm * 0.5 rad\n= 5 cm\n\nAnd this kinda makes sense - if the total circumference is 20pi, and the arc is 28.96 degrees, then the arc length can also be found by\n\narc length = angle * circumference/360\n= 28.96 * 20pi/360\n= 5 cm
182934
You are given only Center (h,k) and radius r. Use the formula:\n(x - h)^2 + (y - k)^2 = r^2\nTransform this into:\nx^2 + y^2 + Ax + By + C = 0\nFor easier substitution.\n\nOr...\n\nWith the center (h,k) and radius r,\n\nPlot the points (h,k + r) (h,k - r) (h + r,k) and (h - r,k)\nThese points will be your guide to draw the circle!!
554627
the circumference of a circle can be calculated by using the formula:\n circumference of circle=2*pie*r\n where pie=22/7;it is equal to 3.1415;\n r=radius of the circle.\nThanks.
808986
y^2 = 1 - x^2\n\ny^2 + x^2 = 1\n\nremember that a circle centered on (x=0,y=0) has the property\n\nx^2+y^2 = r^2\n\nwhere r is the radius\n\nSo your plot is simply a circle arc with radius 1 centered on the origin.