enigma123 wrote:
Attachment:
ABCD.png
Is quadrilateral ABCD a square?
(1) AB = BC = CD = DA
(2) AC = BD
In this question - How come the answer is C?
In Square the diagonals bisect each other at 90 degrees and are equal. How do we know that diagonals are bisecting each other at 90 degrees?
square has equal sides and equal diagonals.
rhombus has equal sides but not equal diagonals.
so both together are sufficient...... Answer (C)
About the 2nd question, let p the point of intersection ofthe two diagonal AC and BD.
now angle PAB = angle PBA [because PA=PB]
so angle APB has to be 90 or it will not be possible for the total angle surrounding the point P to be 360.
so diagonals have to bisect at 90 degress
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75% (00:32) correct 
