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SAT Math 4.2 Geometry and Measurement 278 Views


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Description:

SAT Math 4.2 Geometry and Measurement

Language:
English Language

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…

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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