BrainDen.com - Brain Teasers
• 0

# impossible result

## Question

i cant for the llfe of me find the flaw with his logic.

somewhere between factoring each polynomial and the step before is wrong. but i see no mistake.

• 1

## Recommended Posts

• 1
Spoiler

The error happens when he takes the square root of both sides.

(4-9/2)^2 = (-1/2)^2 = (1/2)^2 = (5-9/2)^2

Or more simply...

(-1)^2 = (1)^2, take the square root of both sides gives -1 = 1.  Except it doesn't!

sqrt((-1)^2) = |-1| = |1| = sqrt(1^2)

• 1
##### Share on other sites
• 0
Spoiler

so you cant say that just because X2 = Y2, X = Y, that would be theoretically incorrect. X2 = Y2 implies that X = |Y| where |a|  or mod(a) denotes +/-a. From there we eliminate the absurdity and only consider the solution for the equation that makes sense

## Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account. ×   Pasted as rich text.   Paste as plain text instead

Only 75 emoji are allowed.

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.