Egyptian Right Angles - Part 2

Geometry Level 1

In ancient Egypt, Asher ( Acenith's assistant) is an apprentice rope stretcher . He's preparing ropes to make a right triangle for laying out a good foundation, and is tying knots in the ropes at equal distances. He leaves one end of the rope unknotted so that each knot corresponds to one unit of length.

Assuming he's tied one rope with 3 knots, and one with 5, how many knots should he tie in the third rope to make a right triangle?

5 4 6 3

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16 solutions

Prasun Biswas
Feb 26, 2014

Since, each knot corresponds to 1 1 unit length and there are 3 3 and 5 5 knots in the two ropes respectively, so the length of those two ropes are 3 3 and 5 5 units respectively.

For the three ropes to make a right triangle, the lengths of the ropes should make a pythagorean triplet. We know that ( 3 , 4 , 5 ) (3,4,5) make a pythagorean triplet as 5 2 = 3 2 + 4 2 5^2=3^2+4^2 . Now, the two ropes have lengths 3 , 5 3,5 respectively. To make the pythagorean triplet and make a right triangle, the third rope must have length 4 4 units and since, each knot corresponds to 1 1 unit length, so number of knots on the third rope = 4 =\boxed{4} .

As the 3 ropes make a right angle triangle , they need to form a pythagorean triplet-----and 3,4,5 form one(5 5=4 4+3*3)

Samarth Mohanty - 7 years, 3 months ago

Ya right that...

Divyam bapna - 7 years, 3 months ago

logically, those ropes have increasing lengths. the shortest one have 3, the longest have 5. what's for the middle length? 4!

Jeco Palay - 7 years, 3 months ago

yes how could i forgrt the pythagoras theorem.

Usama Hassan - 7 years, 3 months ago

\Haaah. I thought that the 30-60-90 theorem would solve this.....

Chester Frias - 7 years, 3 months ago

the moment i saw 3 and 5 i knew the answer is 4- Pythagoras triplets :P

anju rawat - 7 years, 3 months ago

a more simple way to do this problem: a right triangle is a triangle with 3 different sides. 4 is the correct answer because the shortest lenght is the 3 and the longest in 5 what is in between 4 so the answer is 4.

bob jerry - 7 years, 2 months ago
Francis Tibalao
Mar 12, 2014

Assume the missing length is (b) By P.T b²=c²-a²

=5²-3²

=25-9

b²=16

=√16

=4 Answer :)

Asif Iqbal
Mar 9, 2014

3,4,5 FORM A PYTHAGOREAN

Rajat Nair
Mar 7, 2014

3,4,5 FORM A PYTHAGOREAN TRIPLET

using pythagoras therom will be help full to solve the question

Mikku Thomas
Mar 22, 2014

itz simple pythagoras theorem

Vipul Madan
Mar 20, 2014

hypotunese property

David Lancaster
Mar 18, 2014

Its a simple Pythagorean Theorem. Instead of squares they use knots.

Job Triviño
Mar 13, 2014

it must satisfy the relationship between the sides of any triangle which is a+b > and not equal to the remaining side of a triangle.....and since it is a right triangle therefore to find the remaining side it must satisfy the equation c^2 = a^2 + b^2 wherein: 5^2 = 3^2 + 4^2 :)

Cayden Gray
Mar 11, 2014

three squared plus four squared equals twenty-five, the square root of twenty-five is 5

Amer Iliyas
Mar 3, 2014

simple, 5^2 = 3^2 + 4^2....,by phythogrous th.

3.4.5 are sides of right angle traingle

Nav Blaze
Mar 1, 2014

Pythagoras Theorem must be applied in this case.

A.T.Q 1 knot = 1 unit length Side 1 = 5 knots = 5 units Side 2 = 3 knots = 3 units Side 3 = Hypotenuse = x

x^2 = 5^2 * 3^2

x = 4 (on solving)

Ganesh Alat
Feb 28, 2014

as distance between 2 knots are equal so that according to theorem 5^2-3^2=4^2 i.e. answer is 4

Rajat Jain
Feb 28, 2014

using pythagorus theorem for right angle traingle, x^2+3^2=5^2 => x=4

Adeen Shukla
Feb 28, 2014

extremely simple since there are 5 and 3 knots so we know that the length is 5 and 3 units. now use basic middle-school algebra (pythagoras theorem) to get the answer simply as 5^2=x^2+3^2 solve and you get x=4

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