Question

A circle has its center at the origin, and (5, -12) is a point on the circle. How long is the radius of the circle? A.5 B.12 or C.15

Answer 1

easy peasy

a circle centered at the origin is form
x^2+y^2=r^2
r=radius

point (5,-12) is on it
sub to find r^2

(x,y)
(5,-12)
(5)^2+(-12)^2=r^2
25+144=r^2
169=r^2
sqrt both sides
13=r

the radius is 13
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