Grade 7 › G7U07 Circles & Area

Grade 7 › G7U07 Circles & Area › L5
GRADE 7 · ALBERTAOUTCOME AB-G7-SS2

L5 · Area of a circle

Learning goal

“I can find the area of a circle with A = πr^2 using π ≈ 3.14 - squaring the radius first - and if I am given the diameter, I halve it before I start.”

Area — the amount of surface a shape covers, measured in SQUARE units (cm2, m2): how many unit squares fit inside.
r^2 ("r squared") — the radius multiplied by itself: r^2 = r x r. For r = 5, r^2 = 25 - it is NOT 2 x r.
Square units — the unit of area, written with a small 2: cm2. Circumference is a length (cm); area is a covering (cm2). Never mix them.
Worked example

A circle has radius 5 cm. Find its area. Step 1: Picture the square built on the radius: 5 by 5 = 25 cm2. The circle's area is π copies of that square - a little more than 3 of them. Step 2: A = πr^2 = 3.14 x (5 x 5) = 3.14 x 25. Step 3: A = 78.5 cm2. Sanity check: a bit more than 3 x 25 = 75 - it fits, and the unit is cm2, because area is a covering. Say it plainly: SQUARE FIRST, then multiply by π. r^2 means r x r, never r x 2.

Check yourself — explain it

For r = 6, the value of r^2 is...

Paired problem — example still visible

Radius 3 cm -> A = 3.14 x 9 = 28.26 cm2

Faded completion — last step is yours

"Radius 8 cm: A = 3.14 x (8 x 8) = 3.14 x ___ = ___ cm2" -> 64; 200.96 cm2

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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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