How to Prove that AB=2BC without using any of the given angles?

In summary: Is this correct?In summary, the homework statement is that ABCD is a parallelogram.angle DAE=angleEAB and angle CBE=angleEBA . Prove that AB=2BC.
  • #1
1/2"
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Homework Statement


ABCD is a paralleelogram.angle DAE=angleEAB and angle CBE=angleEBA .Prove that AB=2BC


Homework Equations



none

The Attempt at a Solution


I just got that angle AEB =90 degrees
(But it isn't of any help)
Please help !
 

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  • #2


Hey I have worked on a solution but i don't know if it's correct.
If i extend the line AE into EF such that FB=BC
and if angle EAB=y=angle FAD and angle CBA=2x
exterior angle FAG=angle FAD+ angleCBA( corresponding angle as CBIIAD)=y+2x
Also, angle FAD=angleFBA +angleAFB
=> 2x+y=angleFBA+2x =>y=angleFBA
.: As angleFAB= angle AFB
.: AB = FB=>
=>AB=2BC
Is it correct? Please let me know if it is wrong.
 

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  • #3


1/2" said:
Hey I have worked on a solution but i don't know if it's correct.
If i extend the line AE into EF such that FB=BC. FB = FC + BC.
From your second drawing, FB can't possibly be equal to BC. Maybe you didn't say what you meant, but what you said was incorrect.
1/2" said:
and if angle EAB=y=angle FAD and angle CBA=2x
exterior angle FAG=angle FAD+ angleCBA( corresponding angle as CBIIAD)=y+2x
Also, angle FAD=angleFBA +angleAFB
=> 2x+y=angleFBA+2x =>y=angleFBA
.: As angleFAB= angle AFB
.: AB = FB=>
=>AB=2BC
Is it correct? Please let me know if it is wrong.

In your first post you established that angle AEB = 90 deg. You didn't think that was any help, but it is. I worked this problem by labeling all of the interior angles of your original figure.

You are given that DAE = EAB. Let a = the measure of each of these angles. Also, since ABE = EBC, let the measure of each of these angles = b. Since opposite angles of a parallelogram are congruent, ADE = 2b and BCE = 2a.

Now let the measure of DEA = c and the measure of BEC = d. From the fact that the sum of the interior angles of a triangle is 180 deg., you can find c and d, and determine that triangle ADE is isosceles and that triangle BEC is also isosceles. You can also determine that these two triangles are congruent, and once you do that, you can show that AB = 2BC.
 

FAQ: How to Prove that AB=2BC without using any of the given angles?

What is a parallelogram?

A parallelogram is a four-sided shape with two pairs of parallel sides. This means that the opposite sides of a parallelogram are equal in length and never intersect.

What is a parallelogram proof problem?

A parallelogram proof problem is a mathematical problem that requires the use of geometric theorems and proofs to show that a given shape is indeed a parallelogram. These problems often involve proving that the opposite sides and angles of a quadrilateral are equal in length and measure, respectively.

How do I approach a parallelogram proof problem?

The first step in approaching a parallelogram proof problem is to carefully read and understand the given information and diagram. Then, you can use the properties and theorems of parallelograms, such as the opposite sides being parallel and equal in length, to logically prove the given statements. It is also helpful to draw additional lines or angles to aid in the proof.

What are some common theorems used in parallelogram proof problems?

Some common theorems used in parallelogram proof problems include the Opposite Sides Theorem, which states that the opposite sides of a parallelogram are congruent, and the Consecutive Angles Theorem, which states that the consecutive angles of a parallelogram are supplementary. The Pythagorean Theorem may also be used in some problems involving right parallelograms.

Are there any tips for solving parallelogram proof problems?

One helpful tip is to start by labeling the given information and any equal or congruent parts in the diagram. This will help you to see patterns and identify which theorems may be useful in the proof. It is also important to carefully follow the logical steps in the proof, making sure to use the given information and previously proven statements. Finally, practice and patience are key in becoming proficient at solving parallelogram proof problems.

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