The endpoints of one diagonal of a rhombus are (0, -8) and (8, -4). If the coordinates of the 3rd vertex are (1, 0), what are the coordinates of the 4th vertex?

(7, -12)
(7, -8)
(-8, -4)
(-4, -12)

1 answer

Simplest way, just count on the grid ...

you have 3 points, and you know that opposite sides must be parallel and equal
A quick calculation shows that each of the given sides is √65 , so far so good.

For the line from (1,0) to (0,-8) we went one to the left, then 8 down
so from (8,-4) go 1 left, then 8 down to get
(7, -11)

(check by taking the lengths of the new lines, I did,
they were both √65)