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SAT Math 10.4 Geometry and Measurement. What is the perimeter of triangle DEF?
SAT Math 4.2 Geometry and Measurement 278 Views
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Description:
SAT Math 4.2 Geometry and Measurement
- Geometry and Measurement / Transformations
- Product Type / SAT Math
- Geometry / Experiment with transformations in the plane
- Geometry / Understand congruence in terms of rigid motions
- Geometry / Understand similarity in terms of similarity transformations
- Congruence / Experiment with transformations in the plane
- Congruence / Understand congruence in terms of rigid motion
- Similarity, Right Triangles, and Trigonometry / Understand similarity in terms of transformations
- Additional Topics in Math / Right triangle problems (word problems)
Transcript
- 00:02
Here’s your shmoop du jour, brought to you by rotating triangles.
- 00:10
Triangle ABC is rotated 90° counterclockwise about the origin, then reflected over the y axis.
- 00:17
What are the new coordinates of C?
- 00:19
Here are the potential answers...
- 00:24
Who knows why we’re rotating and reflecting this triangle…
Full Transcript
- 00:27
…maybe it was getting stir crazy and wanted a change of scenery.
- 00:30
Whatever the reason, this problem tells us that we must first rotate the sucker 90 degrees about the origin…
- 00:36
…and then reflect it across the y axis.
- 00:40
When we rotate the triangle about the origin,
- 00:42
that means that we have to picture the entire thing on a hinge…
- 00:46
…and that hinge is at zero, zero.
- 00:48
…we just have to imagine that pivot point, and swing the whole thing around from there.
- 00:53
When we do that, our triangle ends up here…
- 00:55
…with point C at (-2, -1).
- 00:59
And now the easy part. When we reflect a shape across an axis, all we do is flip it.
- 01:04
We can see that point C now sits at (2, -1)…
- 01:07
…which is choice E, our final answer.
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