# How to know the coordinates of a point on a circle knowing only the radius?

Hello, I need to find the point marked on the image. Known only to the radius of the circle (=1).
August 19th 19 at 23:10
August 19th 19 at 23:12
Solution
If I understand correctly signed "modulator" in the picture, the angle You have exactly 45 degrees. Then the coordinates of a point :
(sqrt(2)/2 ; sqrt(2)/2)
(0,70711 ; 0,70711)
explain the decision? - madyson16 commented on August 19th 19 at 23:15
x = r*cos(fi)
y = r*sin(fi) - priscilla_Fram commented on August 19th 19 at 23:18
August 19th 19 at 23:14
If you know only the radius, it does.
Now, if it were known, and the angle, that is another matter
something I suspected, thank you. - madyson16 commented on August 19th 19 at 23:17
August 19th 19 at 23:16
x = r*cos(fi)
y = r*sin(fi)
August 19th 19 at 23:18
Well, if the angle is 45, as shown in the figure, the X,Y coordinates of a point the square root of 1/2 by the Pythagorean theorem
that is 0.707, which judging by the picture, seems to be true) thanks - madyson16 commented on August 19th 19 at 23:21
a little more is not a sign? - priscilla_Fram commented on August 19th 19 at 23:24
by : Pythagoras the easiest way. Hold the perpendiculars from a point on the axis X and y, we obtain an isosceles right-angled triangle with hypotenuse of length 1 (because the radius). By theorem, a^2 + b^2 = c^2, that a and b are equal, and c is a unit, we will obtain the equation 2x^2 = 1, from which x = √(1/2) - madyson16 commented on August 19th 19 at 23:27
August 19th 19 at 23:20
A circle is specified by center and radius.
If there is a center, you can find the coordinates of the point.
centre 0;0 - madyson16 commented on August 19th 19 at 23:23
August 19th 19 at 23:22
A circle is an infinite set of points equidistant from the center. Ie a circle is determined by TWO! parameter: the degree of equidistance (radius) and CENTER! Even if we assume that the center coincides with the origin of coordinates as on your picture all one one little radius as the radius defines ENDLESS! the number of points. Need to know the direction vector from the center to the point (see picture). The vector typically is set by an angle in some problems of vector sets straight through the center of a circle and a point outside the circle
August 19th 19 at 23:24
The coordinates of any point on the circle of radius R with center at the origin obey the equality:
x^2 + y^2 = R^2

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