Math questions from any Manhattan Prep GMAT Computer Adaptive Test.
divyagokulnath
Students
 
Posts: 2
Joined: Thu May 07, 2009 4:58 pm
 

please verify :- squares and rhombus

by divyagokulnath Sun Aug 30, 2009 12:27 am

In this Data Suff question, which is there in the geometry question bank

Is quadrilateral ABCD a rhombus?

(1) Line segments AC and BD are perpendicular bisectors of each other.

(2) AB = BC = CD = AD

The answer provided in option (d), which means that either statement alone suffices.
However, even in a square, aren't the diagonals perpendicular to each other?
how can u determine whether the question is about a rhombus or a square?

similarly, from statement 2, AB=BC=CD=AD can happen either in a square or a rhombus

The statement needed is whether the angles are 90 degrees or not...

please verify this question
regards
divya
divyagokulnath
Students
 
Posts: 2
Joined: Thu May 07, 2009 4:58 pm
 

Re: please verify :- squares and rhombus

by divyagokulnath Sun Aug 30, 2009 5:42 am

ok i viewed the reply in one of the other posts :) so every square is a rhombus..
Ben Ku
ManhattanGMAT Staff
 
Posts: 817
Joined: Sat Nov 03, 2007 7:49 pm
 

Re: please verify :- squares and rhombus

by Ben Ku Sat Sep 26, 2009 2:22 am

Yea, students get rhombuses (actually, rhombi) and squares confused all the time, because rhombi are not mentioned much in school.

A rhombus is any quadrailateral with four congruent sides. By that definition, a square is a special type of rhombus (with four congruent angles).

Let me know if there are additional questions.
Ben Ku
Instructor
ManhattanGMAT
Ben Ku
ManhattanGMAT Staff
 
Posts: 817
Joined: Sat Nov 03, 2007 7:49 pm
 

Re: please verify :- squares and rhombus

by Ben Ku Thu Oct 29, 2009 3:04 am

In both the kite and rhombus, the diagonals are perpendicular. However, because the rhombus is a parallelogram, the diagonals also must bisect each other. This is not true for the kite because the kite is not a parallelogram.

(1) is fine because it says the diagonals are "perpendicular bisectors."
Ben Ku
Instructor
ManhattanGMAT
chitrangada.maitra
Course Students
 
Posts: 75
Joined: Thu Feb 25, 2010 2:03 pm
 

Re: please verify :- squares and rhombus

by chitrangada.maitra Sat Aug 07, 2010 1:27 pm

So, its safe to say that the following properties are true:

1. If a quadrilateral has perpendicular bisectors, their opposite angles are equal

2. If the four sides of any quadrilateral are equal, the opposite angles of the quadrilateral will be equal as well.

Because, if the above mentioned does not hold true in all cases, then the quadrilateral cannot be a rhombus.
mschwrtz
ManhattanGMAT Staff
 
Posts: 498
Joined: Tue Dec 14, 2004 1:03 pm
 

Re: please verify :- squares and rhombus

by mschwrtz Thu Sep 02, 2010 5:39 pm

Those two rules are right chitrangada.maitra, but let's make them a bit stronger:

1. The diagonals of a quadrilateral are perpendicular bisectors IF AND ONLY IF its opposite angles are equal.

2. The four sides of any quadrilateral are equal IF AND ONLY IF the opposite angles of the quadrilateral are equal.

By the way, if you can bear with a little math nerdiness, a rhombus is a special kite (i.e., every rhombus is a kite, but not every kite is a rhombus). The diagonals of a rhombus are perpendicular, just like the diagonals of every other kite.

A rhombus is also a special parallelogram. the diagonals of a rhombus bisect one another, just as do the diagonals of every other parallelogram.

If you have a figure that's both a rectangle and a kite, you have a rhombus.