Perimeter, Area and Circle Mensuration: Where to start

Put a fence round a lawn, and you are paying for a length in metres. Cover the same lawn in turf, and you are paying for a space in square metres. That length is the perimeter, the distance all the way round the outside. The space is the area, everything inside the edge. This chapter finds both for flat shapes, first with straight sides, then with curves. Here is what to watch for, and which video to press first.

Everything here is flat, a shape drawn on paper with no depth. The chapter is built to be watched in order, so each video leans on the one before it.

Perimeter means walking the edge and adding every length you pass, curved parts included. Examiners report students who were asked for an area, gave a perimeter instead, and scored nothing. If perimeter and area still blur together, start with Perimeter of 2D and composite shapes. Triangle area needs the perpendicular height, the one that meets the base at a right angle. The common slip is not seeing that the height has to be worked out first. Many students use a length that is not the height at all. If heights catch you out, go to Area of triangles, parallelograms and trapezia. Circles have two formulae of their own, one for the distance round and one for the space inside, and both start from the radius. If those two are not solid yet, go straight to Circle circumference and area. A sector is a slice of a circle, and its angle says what fraction of the circle you have. Examiners report students who used the smaller slice's angle when the question wanted the bigger slice. If circles are fine and slices are the worry, jump to Arc length and sector area, including major sectors. Every course sets perimeter, flat areas and whole circles on Foundation and on Higher. One course keeps sectors to its Higher paper only. Each video can be searched by its name or by its code. The quickest way is the scholafly.com website, which indexes every video in every subject. If you are not sure where you stand, start at the top of the list and work down.

Next in the chapter is Perimeter of 2D and composite shapes. Hopefully that's next in your feed, but if not, search for ScholaFly M A two three, oh one.

Every other video is on scholafly.com too, easy to search by video code or by keyword. Whatever you're revising, go there and have a look, or, watch the next video.