X is on circle O (O is the center) and Y on circle P (P is the center) such that line XY is tangent to both circles. Given that line OP = 40 and the radii of circles O and P are 31 and 7 respectively, find XY.
Sorry I cannot provide an image TvT
The length of XY = sqrt [402 - (31 - 7)2]
The only really important thing that you may not know is that
the tangent to a circle is perpendicular (at right angles) to the radius that it intersects with.