Geometry Problem. Medal & Fan to whoever can help.

- anonymous

Geometry Problem. Medal & Fan to whoever can help.

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- anonymous

Triangle ABC has been rotated 90° to create triangle DEF. Using the image below, prove that perpendicular lines have opposite and reciprocal slopes. You must show all of your work to receive credit.

##### 1 Attachment

- anonymous

find the slope of both lines

- anonymous

If the slope of the first line is 5 then the perpendicular line will be the negative reciprocal which is -1/5

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## More answers

- anonymous

Find the slope for line BC first

- anonymous

Do you know how to do that?

- anonymous

May you remind me how it is done @10115658 . It is getting late where I am currently and my brain is sort of dead. I'm trying to take notes for an exam at the moment so just trying to see how it is solved and write it down.

- anonymous

Pick 2 points on the line

- anonymous

C and B?

- anonymous

Or you mean within the line?

- anonymous

within the line, i'll pick the first one
(1,1)

- anonymous

I suppose we can do (2,2) as well?

- anonymous

i don't think that's a point on the line

- anonymous

what are the coordinates for point B

- anonymous

oh wait you confused me.

- anonymous

(4,5)

- anonymous

Thats right

- anonymous

now we use the slope formula, rise/run

- anonymous

|dw:1432956614754:dw|

- anonymous

1 would be the slope?

- anonymous

wait, i think i did that wrong too.

- anonymous

4/3(?)

- anonymous

4/3 is correct

- anonymous

what would be the negative reciprocal of that?

- anonymous

I apologize, I have not had much time to rest so I see myself making a lot of mistakes.

- anonymous

-0.08(?)

- anonymous

you don't have to apologize, happens all the time

- anonymous

uhhh

- anonymous

ok, what is the reciprocal of 4/3?

- anonymous

i'm getting -0.0833333333 according to google for negative reciprocal.

- anonymous

and then the reciprocal would be 0.08. unless of course there's a formula i'm not remembering.

- anonymous

you don't need a calculator for this

- anonymous

Remind me how we determine it then if you would? Haha

- anonymous

|dw:1432956822160:dw|

- anonymous

.. -facepalm-
3/4
.75

- anonymous

now make it negative

- anonymous

so would it be the same case for negative reciprocal?
-3/4
-.75?

- anonymous

ok, so now we find the slope of the other line. If the slope is -3/4 then we know the lines are perpendicular

- anonymous

so we are looking at EF now?

- anonymous

yes. So do the same thing we did before

- anonymous

First find 2 points

- anonymous

f is -1,1, e is -5, 4.
just from that, i already know they are indeed perpendicular.

- anonymous

yep
(4-1)/(-5-(-1)) = -3/4

- anonymous

Is it that simple to answer the question? Oh my lord, I feel dumb.

- anonymous

once you understand it its simple, same with all math i guess

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