So, the problem in my book (not required, but I wanted to give a crack at it) is
In this lesson you learned that $m = \frac{y_2-y_1}{x_2-x_1}$. Use an algebraic proof to show that the slope can also be calculated using the equation $m = \frac{y_1-y_2}{x_1-x_2}$.
We haven't learned proofs yet (this is geometry I'm in) so I have very little clue what I'm doing. Here are my thoughts so far:
- Do a proof by contradiction? (I have a vague idea of what this and other types of proofs are, so I could be wrong on this)
- Something to do with negatives canceling out is the reason
- Something to do with squaring, perhaps?
Otherwise, I really don't know where to start. Any hints would be appreciated at how to begin, or even basic things to prove before doing this.
Thanks!
Just pull out a factor of $-1$ from both numerator and denominator and what do you get?