construct rotation image of triangle

J

jazziza87

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Apr 2, 2006
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Can anybody help me?

I have a math problem that asks me to construct the rotation image of a triangle under a 90 degree counterclockwise rotation about a point R. And it tells me to use only a protracter and a ruler. Could someone explain me how to work out this problem.

Thanks in advance!
 
Re: rotation

Hello, jazziza87!

The directions are clear and straight-forward.
Exactly where is your difficulty?

Construct the rotation image of a triangle under a 90<sup>o</sup>CCW rotation about a point R.

Use only a protracter and a ruler.
Click to expand...
Code: 
     A'
      o

        *                 A 
                        o
          * 90°     *
                *
            o
            R

Measure distance \(\displaystyle RA.\)
Use the protracter to determine a direction 90<sup>o</sup> CCW from \(\displaystyle RA.\)
Locate point \(\displaystyle A'\,\) so that \(\displaystyle \,RA'\,=\,RA.\)

Do the same for points \(\displaystyle B\) and \(\displaystyle C.\)
 
I'm sorry I meant to say I am not allowed to use a protractor, I am only allowed to use a ruler and a compass. I don't understand how to do it with just a compass.

Thanks for your help.
 
Are you saying “use only a straightedge and compass?
OR, are you saying “use only a compass?
Which is it?
 
jazziza87 said:
I am only allowed to use a straightedge and a compass.
Click to expand...
Well, to rotate any point about R use soroban’s method as shown in his reply.
With a straightedge and a compass construct the line AR and at the point R construct a perpendicular to AR, call it SR. Using the compass mark of on SR a distance equal to RA, call that point A’.

Now, to rotate a triangle one must rotate each of its vertices in this manner.
 
Geometry

Hey pka I looked up on the internet what Soroban's method is but I could'nt find any definition on how to use it. Could you explain what it is just a bit more. Thanks for all your help
 
Using a straightedge and compass all of the constructions are absolutely standard!
Are you really in a study of basic geometry? It hard to believe you that are!

Any, any geometry textbook has these constructions: Using a straightedge and compass,
1) given a point on a line construct a perpendicular to the line at the point.
2) given any two points construct a circle centered at one passing thru the other.

Those are the only two constructions you need to follow my instructions. If this is impossible for you to follow and do, I don’t think it is worthwhile for you to pursue this question here.
 
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