Steph's Friend

Wednesday, November 30, 2005

Maths Trivia

See if you can spot what's wrong with these equations...

1)

4 - 10 = 9 - 15
Add 25/4 on both sides
4 - 10 + 25/4 = 9 - 15 + 25/4
(2 - 5/2) (2 - 5/2) = (3 - 5/2) (3 - 5/2)
Taking square roots
(2 - 5/2) = (3 - 5/2)
2 = 3

Can you explain why?

2)

Let X = Y
X - Y = 0
Therefore,
2X - 2Y = 0
So,
2X - 2Y = X - Y
2 (X - Y) = (X - Y)
Dividing by (X - Y) on both sides,
2 = 1

Can you explain why?

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6 Comments:

Blogger Euian said...

for no.2, if (x-y)=0 then, you are dividing both sides by zero which is illegal in mathematics so the equation is false.

I'm too lazy to do manual calculation for no. 1.

12:00 AM, December 01, 2005  
Blogger jane said...

OH
MY
GAWD
it's 2:12 AM
MY BRAIN IS FRIED
BUT THANK YOU
FOR THE CHALLENGE
:)

6:12 PM, December 01, 2005  
Blogger Steph said...

Euian,

You are right about the second one. As for the first one...lol...the answer is there. Just read carefully :D

6:12 PM, December 02, 2005  
Blogger Steph said...

Jane,

Haha...glad that you are still working ur brains at such an hour. Hope that you find the teasers fun :)

6:13 PM, December 02, 2005  
Anonymous Anonymous said...

for teaser number 1

the fact is maths is that the square root of a number is always > 0.
hence sqrt(4)=2 and sqrt(9)=3

In puzzle 1....the calculation is perfect all the way till the stage
sqr(2-5/2) = sqr(3-5/2)
now when we take the root of both sides,
sqrt(sqr(3-5/2)) = 3-5/2
but sqrt(sqr(2-5/2)) = 5/2-2 (because 2-5/2 is negative and can't be a result of a sqrt operation.)

You can check for yourself that
5/2 - 2 = 3 - 5/2

Cheers
Aniruddha

10:49 AM, December 05, 2005  
Anonymous Anonymous said...

for teaser number one aniruddha is wrong since we are not taking square root of any negative number,but of a square whose roots are negative.
for eg.
the sqr root of 1 is -1 or 1;
hence the sqr root of sqr(2-5/2)
can be negative.

11:10 PM, November 07, 2006  

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