Circle A has a radius of 2 and a center of (5,7). Circle B has a radius of 4 and a center of (3,2). If circle B is translated by <2,1>, does it overlap circle A? If not, what is the minimum distance between points on both circles?

1 Answer
Oct 25, 2017

circles touch externally

Explanation:

What we have to do here is compare the distance (d) between the centres of the circles to the sum of the radii

if sum of radii>d then circles overlap

if sum of radii<d then no overlap

We require to find the 'new' centre of B under the given translation which does not change the shape of the circle only it's position.

under a translation <2,1>

(3,2)(3+2,21)(5,1) new centre of B

Note that the x-coordinate of the centres of both circles is 5 indicating that they lie on the vertical line x = 5
Hence d is the difference in the y-coordinates.

d=71=6

sum of radii =2+4=6

since sum of radii =d=6

then the circles touch externally
graph{((x-5)^2+(y-7)^2-4)((x-5)^2+(y-1)^2-16)=0 [-20, 20, -10, 10]}