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Rotate A(2, 1) B(4, 1) C(4, 2) 180° about the origin, then translate…

Step by step, with the reason for every step · Two moves in a row · Geometry

Step by step

The question

Question: rotate the shape A(2, 1), B(4, 1) and C(4, 2) 180°, then translate it right 3, up 1.

A(2, 1), B(4, 1) and C(4, 2)
= rotate 180° about O,
= then translate right 3, up 1

1 Draw the shape

Put the points on the grid and join them.

2 First: rotate 180°

Rotation 180°: both numbers stay in their places, and both change sign.

The rule is: (x, y) goes to (−x, −y).

(x, y) → (−x, −y)

A(2, 1) goes to A'(−2, −1).

A(2, 1) → A'(−2, −1)

B(4, 1) goes to B'(−4, −1).

B(4, 1) → B'(−4, −1)

C(4, 2) goes to C'(−4, −2).

C(4, 2) → C'(−4, −2)

Join them.

This is the first image.

3 Then: translate

Translation right 3, up 1: right 3 adds 3 to x, up 1 adds 1 to y.

The rule is: (x, y) goes to (x + 3, y + 1).

(x, y) → (x + 3, y + 1)

A'(−2, −1) goes to A''(1, 0).

A'(−2, −1) → A''(1, 0)

Careful!

The second move starts from the new points A', B' and C'.

Not from the first shape.

Careful: start from A', not from A

B'(−4, −1) goes to B''(−1, 0).

B'(−4, −1) → B''(−1, 0)

C'(−4, −2) goes to C''(−1, −1).

C'(−4, −2) → C''(−1, −1)

Join them.

This is the final image.

So the final image is A''(1, 0), B''(−1, 0) and C''(−1, −1).

A''(1, 0), B''(−1, 0) and C''(−1, −1)

4 Check

Let's check in one go.

Put the first rule's answer (−x, −y) into the second rule.

We get (−x + 3, −y + 1).

(x, y) → (−x, −y) → (−x + 3, −y + 1)

A goes straight to (1, 0).

That is A''.

Right!

A(2, 1) → A''(1, 0)

Let's look back.

First: draw the shape.

Then: rotate 180°.

Then: translate right 3, up 1.

Last: check.

Answer
A''(1, 0), B''(−1, 0) and C''(−1, −1)

Your turn

Try this one yourself, then check:

A(3, 2) B(5, 2) C(5, 3): rotate 180° about O, then translate right 4, up 1
Show the answer
A''(1, −1), B''(−1, −1) and C''(−1, −2)

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