## enya.gold 2 years ago Need a confirm, please. Am I doing this right?

1. enya.gold

2. enya.gold

I would use my trusty Distance Formula, although I'm not sure which is which to plug in.

3. enya.gold

$d = \sqrt(x _{2} - x _{1})^2 + (y _{2} - y _{1})^2$

4. enya.gold

$d = \sqrt (a - (-b)^{2} + (0 - c)^2$

5. tkhunny

What is it that you are trying to do? Perimeter? Area? Other?

6. enya.gold

"Find the lengths of the diagonals of this trapezoid."

7. tkhunny

Okay, first, we should observe symmetry and decide that the two diagonals are the same length. Agreed?

8. enya.gold

Yes.

9. tkhunny

Super. Now, it appears you started working with (a,0) and (-b,c). It also appears that you are having some notaiton problems. That's probably why you are struggling with it. There are parentheses missing. $$d = \sqrt{(a-(-b))^{2} + (0-c)^{2}} = \sqrt{(a+b)^{2}+(-c)^{2}}$$ That's what you had, it's just written with all the symbols int eh right places. Can we do nything else with it?

10. enya.gold

Eh, no, that's precisely what I had in mind! :)

11. enya.gold

Thank you.

12. tkhunny

We might be able to do one more thing. Draw a perpendicular line from (b,c) down to the x-axis. You should see a right triangle. Can we say anything about the relationship of a, b, and c because of this right triangle?

13. enya.gold

|dw:1357966403862:dw| My drawing is not entirely accurate, but I only see a scalene triangle and equilateral triangle?

14. tkhunny

No, no, that't not perpendicular to the x-axis. It should hit the x-axis at (b,0), not at (0,0). It is a vertical line segment.

15. enya.gold

|dw:1357966687931:dw|

16. tkhunny

That's it. The one on the right is the one I was looking for. Anyway, my little right triangle leads to $$(a-b)^{2} + c^{2} = (a-b)^{2} + (-c)^{2}$$ and we don't manage to learn anything, so let's just let that go. It can be very useful to poke around a little. In this case, we didn't learn much, but it was worth the effort to learn to communicate better. :-)