Area of plane figures
Three formulas — triangle, parallelogram, trapezoid — and one rule that governs all of them: the height is perpendicular to the base you chose. A slanted side is not a height. For a trapezoid, a and b are the two parallel sides, not the legs. Students decompose composite figures into these pieces and compute shaded regions as whole minus hole. Fractional dimensions are expected. The hardest items mark the height on a different side from the one students expect.
Specification · for a parent or teacher
- area-triangles-trapezoids
- Advanced Math 6 · Unit 11
- High School Math 1
- Shapes
- 3 of 4 — Grade 6–7 core. Multi-step, first symbolic work.
- 5 items
Students can
use those three; decompose composites; shaded-region (whole minus hole).
Ready when
a shaded region that is a parallelogram minus a triangle, with the height marked on a different side than students expect.
Formulas
a and b are the parallel sides.
Watch for
slanted side used as height; trapezoid and as the legs.