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Quadrilaterals and Polygons

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20180802 192157

Unable to solve 

TG Team 02/08/2018 7:33 pm

Hint : Area Base Ratio - Ratio of area of triangles having base on the same line and third vertex common is equal to the ratio of length of bases of the triangles

TG Team 02/08/2018 10:20 pm

Solution : 

IMG 20180802 221223
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Hey Sir, help me solve this problem.

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Both questions.

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This post was modified 6 years ago by Richa
aniket prajapati 08/08/2018 3:34 pm

In 2nd question. 

Just square the sides given ,add them and see the sum will be square of 73

For example u can consider a triangle or sqaure or hexagon u will get same result ..

TG Team 08/08/2018 4:15 pm

Approach for third question : 

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aniket prajapati 08/08/2018 4:23 pm

Sir, in third question they should tell that assuming there is no slag . shouldn't they ?

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The length of 3 sides of a convex quadrilateral are 4cm, 8cm, and 16cm. How many positive integer values can the fourth side (in cm) take if no two sides have the same length?

A. 23
B. 19
C. 21
D. 24

TG Team 13/08/2018 11:14 pm

Sum of any three sides in a quadrilateral is greater than the fourth side

so 4 + 8 + 16 > n

28 > n .... (1)

also , 4 + 8 + n > 16

n > 4 .... (2)

From (1) and (2)

28 > n > 4

Hence , { 5,6,7,8,....., 27} - { 8 , 16}

21 integral values .

Richa 14/08/2018 1:03 am

Hi Sir, thank you for this. I did it using another approach.  I first divided the quadrilateral into 2 triangles and then used the property of the sum of two sides greater than the third. This way, I got the range of the diagonal of the quadrilateral and then the range of the fourth side. But I am getting a total of 19 values. Attaching my method below.

Can you please point out the mistake in my method?

quad
TG Team 14/08/2018 1:50 am
This post was modified 6 years ago by TG Team

Here,  y need not be an integer . 

So maximum integral  x  = 27 ( when 12 > y > 11)  and minimum integral x = 5 

 

5 - 27 , 23 values

Richa 14/08/2018 2:18 am

Oh! okay. Got it now. Thank you.

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geo

Sir, how do we know that A,B,E,D are concyclic points (as mentioned in the solution)?

TG Team 17/08/2018 12:33 pm

Angle DAB = 90 , Angle AEB = 90 : Angles subtended by  BD are equal so points  A,E,B, D are concyclic points. 

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A regular polygon has interior angles of 168°. How many sides does the polygon have ? 

A regular polygon has an interior angle that measures 144° , and a side of which is 12 units long . What is the perimeter of the regular polygon ? 

TG Team 18/08/2018 11:05 pm

Sum of all interior angles = ( n -2) × 180° 

 

[(n -2) × 180° ]/n = 168° 

 

(n -2 ) × 180 = 168n 

 

12n = 360° 

 

n = 30

TG Team 18/08/2018 11:09 pm

Alternate Approach : 

 

Each exterior angle : 180 - 168 = 12° 

 

We know sum of all exterior angles  of a polygon is always 360°

 

So , 360/12 = 30 exterior angles. 

Hence number of sides = 30 . 

TG Team 18/08/2018 11:11 pm

For 2nd problem : 

 

Each exterior angle 180 - 144 = 36 

Number of sides = 360/36 = 10

 

Perimeter of the polygon : 10 × 12 = 120 units 

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20180824 072924
TG Team 24/08/2018 2:31 pm

PFA the solution 

 

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dd
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Hello sir, Please share the solution to this problem -

In a quadrilateral ABCD , AB is parallel to CD. AB= 8 cm , BC = 10 cm ,CD = 16 cm and AD =10 cm. Find the sum of the lengths of the diagonals. 

TG.Raman 01/09/2018 5:39 pm

 

Hello Nikita , PFA the solution . 


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Hello sir, please share the solution to this problem -

IMG 20180905 220532 EDIT 1
TG Team 05/09/2018 11:13 pm

Hi Nikita , 
PFA the solution 

geo solution
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In a regular polygon of ‘n’ sides, a circle of radius r is inscribed and another circle of radius R is circumscribed. Which of the following is definitely true?

 

 

R/r > 1

R/r < 2 

R/r ≤ 2

1 < R/r ≤ 2

aniket prajapati 12/10/2018 11:09 pm

for instance take a equilateral triangle r=a/2√3 and R=a/√3

R/r=2.................(1)

now take a square r=a/2 and R=a√2/2

R/r=√2=1.414 ...................(2)

from 1 and 2

1 < R/r ≤ 2 

hence option (4)

 

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Three identical squares with bases AP, PQ, and QB are put next to each other to form a rectangle ABCD. Find the sum of the angles <APD + <AQD + <ABD.

60

75

90

120

TG Team 13/10/2018 11:34 am

 

 

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snips
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Hello Sir , kindly share the solution to this problem -

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TG Team 19/10/2018 4:44 pm

Hi Nikita , 

Please go through this link :  https://artofproblemsolving.com/wiki/index.php?title=British_Flag_Theorem

This theorem is valid irrespective of whether P  inside/Outside or the boundary of the rectangle . 

Nikita Chawla 19/10/2018 5:34 pm

Thank you sir  🙂 .Got the correct answer using this 

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TG Team 25/10/2018 5:24 pm

PFA the solution: 

 

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