Chapter 9: Areas of Plane Figures
3 lessons
Areas of Plane Figures extends familiar formulas — squares, rectangles, triangles — to polygons built from combinations of simpler shapes, plus circles and sectors. The method throughout is the same: break an irregular figure down into pieces with known formulas, then add the pieces together.
The habit that matters most
Decomposing a complex shape into simple pieces is reused in every later measurement chapter, right through Surface Area and Volume later this year and into Class 9 and 10's mensuration work — an L-shaped room, for instance, is really just two rectangles whose areas get added.
Double-counting a piece, or leaving a gap between pieces, is the most common error when splitting an irregular figure — the pieces need to account for the whole shape with no overlap and nothing missing.