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

## Main Question or Discussion Point

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.

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CRGreathouse
Homework Helper
You divide by zero in the last step.

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exk
what he said ^

rock.freak667
Homework Helper
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)....

Cool! you got it!
the trick was to know that dividing by zero is impossible.

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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"

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.

Well they're half-right.

rock.freak667
Homework Helper
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!