Grade 4 › G4U09 Area & Angles

Grade 4 › G4U09 Area & Angles › L4
GRADE 4 · ALBERTAOUTCOME AB-G4-4M2

L4 · Angles: Degrees and the Four Classes

Learning goal

“I can describe an angle by its measure in degrees, and I can classify any angle up to 180° as acute, right, obtuse, or straight by comparing it with the 90° right-angle benchmark.”

Angle — the amount of turn between two lines (rays) that meet at a point; also the opening between them.
Degree (°) — the unit for measuring angles. One degree is 1/360 of a full circle: a full turn is split into 360 equal degrees.
Vertex — the point where the two rays of an angle meet.
Right angle / straight angle — a right angle measures exactly 90° (the corner of a book); a straight angle measures exactly 180° (a straight line - a half turn).
Worked example

We measure how wide an angle opens, in degrees. Step 1: A full turn (all the way around a circle) is 360°. So 1° is 1/360 of a full turn. Step 2: A quarter turn - the corner of a book, the corner of this page - is 360 / 4 = 90°. That is a right angle, and it becomes our benchmark: the angle we compare all others to. Step 3: A half turn makes a straight line: 360 / 2 = 180°. That is a straight angle. Say it plainly: every angle measure up to 180° is judged against 90°. Less than 90, exactly 90, between 90 and 180, or exactly 180.

Check yourself — explain it

The right angle (90°) matters so much because...

Paired problem — example still visible

How many degrees is a quarter of a full circle, and what is that angle called? -> 90°, a right angle

Faded completion — last step is yours

"A straight angle is a half turn: 360 / 2 = ___°, so a straight angle measures ___°" -> 180; 180

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10 scored questions with a 3-rung hint ladder. Mastery needs 8/10 plus both gate questions.

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