I came out with the right answer, but did I work this out correctly?

-7y = 0

-7y/-7 = 0/-7

-y = 0

-y/-y = 0/-y

y=0

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- Mar 3rd 2006, 06:23 AMEuclid Alexandria-7y = 0
I came out with the right answer, but did I work this out correctly?

-7y = 0

-7y/-7 = 0/-7

-y = 0

-y/-y = 0/-y

y=0 - Mar 3rd 2006, 07:45 AMearbothQuote:

Originally Posted by**Euclid Alexandria**

you have made only a minor mistake:

-7y/-7 = 0/-7

y = 0

because -7y/-7 = +y the last two lines aren't necessary (and slightly wrong).

Greetings

EB - Mar 3rd 2006, 08:23 AMAradesh
also going from

$\displaystyle -y = 0$

and you then said

$\displaystyle -y/-y = 0/-y$

this is not equivalent to:

$\displaystyle y=0$

as you said.

you had $\displaystyle -y=0$

so what you want to do here to get the solution is divide both sides by $\displaystyle -1$

$\displaystyle -y/-1 = 0/-1$

$\displaystyle y=0$

since it turns out $\displaystyle y=0$

before you were trying to say $\displaystyle -y/-y$ which is $\displaystyle 0/0$ which is undefined. - Mar 4th 2006, 07:45 AMEuclid Alexandria
Thanks, guys. I couldn't remember the rule for getting a negative variable to be positive. You always divide both sides by -1?

- Mar 4th 2006, 05:42 PMAradesh
you could either divide by -1, multiply by -1, the effect is the same. you don't tend to think of it as "multiplying/dividing by -1" though. you just change the sign of both sides. for instance if

$\displaystyle -x = -4$

then

$\displaystyle x = 4$

you are simply changing the sign of both sides. you don't really need to explain yourself when doing that :)

likewise if you had

$\displaystyle -y=17$

then changing the signs of each side gives:

$\displaystyle y=-17$

however multiplying through by -1 is a more common way of thinking about it than dividing through by -1. - Mar 5th 2006, 03:50 AMtopsquarkQuote:

Originally Posted by**Aradesh**

-Dan