Geometrical constructions — measure/draw, SSS triangle, nets

Drawing freehand, or a plain line with no arcs, scores nothing even if it looks right.

When constructing a triangle from three sides, the two arcs must be centred on the ENDS of the drawn base, with radii equal to the other two given sides — not from arbitrary points. Wrong centres give the wrong triangle.

In an SSS construction, set each compass radius to the correct given side length using the ruler before drawing the arc. A mis-set radius (reading off the wrong side) puts the third vertex in the wrong place.

A net must show every face exactly once, correctly sized, so it folds up to the solid. A common error is a missing face, a duplicated face, or faces placed so the shape cannot close up.

With a scale such as $1\text{ cm}$ to $100\text{ m}$, divide a real distance by $100$ for the drawn length, and multiply a drawn length by $100$ for the real distance. Doing it the wrong way is out by a factor of the scale.