Answers

2014-06-08T16:32:17+05:30
Let us consider the points to be A(-1,1); B(0,0)  ; C(3,3) ; D(2,4) 
The distance b/w AB = √(0+1)²+(0-1)² = √2
The distance b/w BC = √(0-3)²+(0-3)² = √9+9 = √18 
The distance b/w CD = √(2-3)² +(4-3)² = √2
The distance b/w DA = √(-1-2)²+(4-1)² = √18
The distance b/w AC = √(3+1)²+(3-1)²=√20
The distance b/w BD = √(2-0)²+(4-0)²=√20
As the opposite sides AB=CD and BC=DA and the diagonals AC=BD
There the quadrilateral which is formed by the points A,B,C,D is a rectangle.
Hence proved. 
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2014-06-08T16:35:14+05:30
Yes they form sides of a rectangle
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