# Two points on a circle

1. Oct 31, 2005

### blimkie

http://putfile.com/pic.php?pic=10/30314175469.jpg&s=x11

if anyone would like to explain this to me that would be excelent and most appreciated

i know that a and b are both "yes" but i i dont know why or how to explain it

thanks
kyle

Last edited by a moderator: Apr 21, 2017
2. Oct 31, 2005

### Tide

How, exactly, do you know both a and b are "yes?"

3. Oct 31, 2005

### mathmike

wouldnt point c be on the circle if points a and b were seperated a certain distance

4. Oct 31, 2005

### daniel_i_l

Lets call OC the x axis and the y axis is perpendicular to it. since the y components will always cancel out, the length of OC will be the sum of the X components of each vector (OA,OB). For OC to be on the circle its length has to be equal to the radius, so OC will be on the circle if the sum of OA's and OB's x components equal r (radius), for example if they each make a 60 deg. angle with the x axis (.5r + .5r = r). For OC to lie inside the circle its length has to be less than r, this can happen if the sum of the x components is less than r, for example, OA and OB each make a more than 60 deg. angle with the x axis.

5. Oct 31, 2005

### blimkie

thanks alot daniel_i_l that explains it better than i could