Geometry A hub · 02.00

Transformations and Congruence

A map of Module 02. Same ideas as Canvas, taught as moves on a plane.

What this module is for

Module 01 was about naming pieces and proving lines and angles. Module 02 is about moving a whole figure and then proving two figures match.

Three moves keep size and shape: slide, flip, turn. Canvas calls those rigid motions. After a rigid motion, the new figure is congruent to the old one.

Then the module uses that idea on triangles and quadrilaterals: SSS, SAS, ASA, AAS, HL, and the parallelogram theorems.

Words that will keep showing up

Pre-image is the original figure. Image is where it lands. A' is read "A prime."

A mapping is written with an arrow: A → A'. The same letters stay matched, in the same order.

A rule is a function for every point: plug in (x, y), get the new ordered pair. Every vertex of a figure uses the same rule, or the two figures would not stay congruent.

Lookalike trap: "orientation changed" does not mean "not congruent." A reflection flips the naming direction (clockwise vs counterclockwise) and still keeps side lengths and angle measures. Congruent is about size and shape, not which way the letters travel.

How quizzes in this module like to ask

Expect the same move as 01.06: two answers share a number, and the discriminator is the reason. Here the "number" is often an ordered pair.

Point P is at (3, −2). These four rules all spit out something that looks nearby:

(x, y) → (x, −y)   reflect over the x-axis → (3, 2)
(x, y) → (−x, y)   reflect over the y-axis → (−3, −2)
(x, y) → (y, x)   reflect over y = x → (−2, 3)
(x, y) → (y, −x)   90° clockwise around the origin → (−2, −3)

If you only remember "swap and change a sign," you will pick the wrong swap. Name the move first, then apply the rule.

Lesson map

Use the hub pages in this order. The pretest on Canvas is 1 point. It is a preview, not the grade that matters.

  1. 02.01 Translations and reflections (rules as functions)
  2. 02.02 Rotations around the origin
  3. 02.03 Rigid motion and triangle congruence (SSS, SAS, ASA, AAS, HL, CPCTC)
  4. 02.04 Triangle proofs (sum, isosceles, midsegment, medians)
  5. 02.05 Activity (short walkthrough of what to submit)
  6. 02.06 Quadrilateral proofs (parallelogram properties)
  7. 02.08 Review and practice test

02.10 is the actual module test. Practice here. Take that one in Canvas.

Naming note: older checklists in the course files still list Translations and Reflections as two separate lesson numbers. On Allie's Canvas they are one lesson, 02.01.

Quick check

Name the move, not just the ordered pair.