2788.21 – Circle through (1989,y)
In a rectangular coordinate plane, any circle which passes through (-2,-3) and (2,5) cannot also pass through (1989,y). What's the value of y?
This is about the fact that no three points on a circle can be collinear.
So we find the equation, , of the line containing (-2,-3) and (2,5).
. so and .
Note: this problem was probably first used in the year 1989. It could be adapted for the current year, of course, or generalized for the year n.