L6 · Plotting and describing points and polygons

Learning goal

“I can plot a set of points on the Cartesian plane, join them in order to form a polygon, name the polygon, describe a plotted polygon by listing its vertices, and count grid units to find the lengths of its horizontal and vertical sides.”

Plot — to mark a point on the plane at its ordered pair.

Polygon — a closed shape made of straight sides (triangles, quadrilaterals, pentagons, ...).

Vertex — a corner of a polygon; a polygon's vertices are listed in order around the shape (plural: vertices).

Perimeter — the total distance around a shape: the sum of all its side lengths.

Worked example

On a plane with axes 0-10, plot A (1, 1), B (5, 1), C (5, 4) and D (1, 4). Join A to B, B to C, C to D, and D back to A. Step 1: Plot each point: across, then up. Step 2: Join them IN THE ORDER GIVEN, and close the shape by joining the last point back to the first. Skipping the closing side is the classic unfinished polygon. Step 3: Name it. The shape has 4 vertices and 4 sides; opposite sides match (bottom and top both run from x = 1 to x = 5; the sides both run from y = 1 to y = 4), and the corners are right angles. It is a rectangle.

Check yourself — explain it

After joining the last point, you must also...

Paired problem — example still visible

Plot (2, 2), (6, 2) and (2, 5), joining in order and back to the start. What polygon appears? -> A triangle (3 vertices joined, closing from (2, 5) back to (2, 2)) - a right triangle with its right angle at (2, 2).

Faded completion — last step is yours

"Points (3, 1), (7, 1), (7, 6), (3, 6) joined in order form a quadrilateral. Its name, from its matching opposite sides and right angles, is a ___" -> rectangle

Ready to practise?

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

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