Posted by **Anonymous** on Friday, December 28, 2012 at 11:46am.

prove that the points (2,-1) (0,2) (2,3)and (4,0) are the coordinates of vertices of a parallelogram and find the angle between its diagonals

- maths --plse help me.. -
**Steve**, Friday, December 28, 2012 at 5:04pm
If we label the points ABCD as given, then

AB and CD have slope -3/2

AD and BC have slope 1/2

so, the sides are parallel

AC is vertical

BD has slope -1/2

so, tanθ = 2 ==> θ = 63.4°

The calculations are easier if you plot the points and draw the diagonals.

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