A Parallelogram with sides of equal length is called a rhombus. Show that the diagonals of a rhombus are perpendicular.

So, I start with v and u which are perpendicular vectors. v + w is a diagonal of the rhombus.

I am not sure how to get the other one, or to solve this question, really.

I know that in order for two vectors to be perpendicular then the dot product must be 0.

so I guess, I need both diagonals and to see if their dot product is zero?