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Q.

A quadrilateral whose diagonals are equal and bisect each other at right angles is called a:


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a

Rhombus

b

Square

c

Rectangle

d

Trapezium

answer is B.

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Detailed Solution

Concept- We’ll use the given property of quadrilateral and prove any unique property of quadrilateral by using the triangle similarity property, congruence rule and by its congruence property.
Let’s assume a quadrilateral ABCD whose diagonals are AC and BD intersecting each other at O.
Question Image       Diagonals AC and BD are equal and bisect each other at 90° .
So,
AC= BD
OB= OD
OA= OC
and
AOB=BOC=COD=AOD= 90°
In AOB and COD
AO= CO (Diagonals bisect each other)
OB= OD(Diagonals bisect each other)
AOB=COD= 90°(Vertically opposite angles)
From the SAS (side angle side) congruence rule, AOBCOD
So, by the property that is referred as CPCT (Corresponding parts of congruent triangles)  AB=CD
OAB=OCD
OAB=OCD are the alternate interior angles of line AB and CD and alternate angles are equal when the lines are parallel to each other.
So, ABCD
From the above equations,
ABCD is a parallelogram.
In AOD and COD
AO= CO(Diagonals bisect each other)
OD= OD(Common)
AOD=COD= 90°
From the SAS (side angle side) congruence rule, AODCOD
So, via CPCT
AD=DC
However AD=BC and AB=CD due to the opposite sides of parallelogram ABCD.
So, AB=BC=CD=DA
Therefore, all the sides of the quadrilateral are equal to each other.
In ADC and BCD
AD= BC(proved)
AC= BD(Given)
CD=CD(Common)
From the SSS (side side side) congruence rule, ADCBCD
Again, through CPCT
ADC=BCD
The ADC and BCD are co- interior angles.
ADC+BCD=180°
ADC + ADC=180°
2ADC=180°
ADC=90°
One of the interior angles of the quadrilateral is right angle.
So, we have obtained that ABCD is a parallelogram, AB=BC=CD=DA and one of the interior angles is right angle.
So, the quadrilateral ABCD is a square.
Hence, the correct option is 2) square.
 
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A quadrilateral whose diagonals are equal and bisect each other at right angles is called a: