4=3 True or False? Check it out and guess where's the mistake!

  • Thread starter kthouz
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  • #1
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Let say that a+b=c
this can be writtem as
4a-3a+4b-3b=4c-3c
by arranging
4a+4b-4c=3a+3b-3c
taking out the constants
4*(a+b-c)=3*(a+b-c)
So 4=3



The mistake is that .... I'll post it soon. i read this from a notebook of my little brother and i firstly agreed to it but by the time i found out why not! Test your knowledge too.
 

Answers and Replies

  • #2
CRGreathouse
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You divide by zero in the last step.
 
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  • #3
exk
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what he said ^
 
  • #4
rock.freak667
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4*(a+b-c)=3*(a+b-c)
So 4=3
You can't divide by a+b-c since a+b=c (i.e. a+b-c=0)....
 
  • #5
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Cool! you got it!
the trick was to know that dividing by zero is impossible.
 
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  • #6
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I remember my dad showed it to me when I was in 5th or 6t grade. It stumped me, and I showed it to my Math teacher at school who explained the 11th Commandment to me: "You shall never divide by Zero"
 
  • #7
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Let say that a+b=c
this can be writtem as
4a-3a+4b-3b=4c-3c
by arranging
4a+4b-4c=3a+3b-3c
taking out the constants
4*(a+b-c)=3*(a+b-c)
So 4=3



The mistake is that .... I'll post it soon. i read this from a notebook of my little brother and i firstly agreed to it but by the time i found out why not! Test your knowledge too.
This is exactly why you never ever divide by a variable. It is horrendous algebra.


x^2=4x


What is x?

75% of students will divide by x and say x=4.
 
  • #8
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Well they're half-right.
 
  • #9
rock.freak667
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This is exactly why you never ever divide by a variable. It is horrendous algebra.


x^2=4x


What is x?

75% of students will divide by x and say x=4.
Then those 75% should always remember that you can only divide by something only if it is not equal to zero!
 

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