Hello,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).
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
you are simply changing the sign of both sides. you don't really need to explain yourself when doing that
likewise if you had
then changing the signs of each side gives:
however multiplying through by -1 is a more common way of thinking about it than dividing through by -1.
Actually I've found that the most common, and difficult to find, mistakes are due to sign errors. I recommend (though don't force) my students to show every step for that reason, even if it seems trivial to do so. I find it makes for good technique.Originally Posted by Aradesh