Posted by dave on .
show that (1,1), (9,4), (20,6) and (10,1) are the vertices of a rhombus and then find the area of this rhombus?

precalculus 
Reiny,
no they are not
just sketch it and find the slopes of the lines, none are equal
In a rhombus opposite sides should have the same slope and they must be equal in length.