Expressions, equations & relationships · TEKS 7.9C
Area of composite figures
Break a strange shape into rectangles, triangles, trapezoids and parts of circles. Add the pieces, or subtract a cut-out.
Key steps
- Rectangle/parallelogram: A = bh. Triangle: A = ½bh.
- Trapezoid: A = ½(b₁ + b₂)h.
- Semicircle: ½πr². Quarter circle: ¼πr².
- Add pieces; subtract holes.
Worked example
A 10 × 6 rectangle with a triangle on top (base 10, height 4). Area?
- Rectangle: 60. Triangle: ½ × 10 × 4 = 20.
- Answer: 80 square units
Watch out: Don’t count a shared edge twice, and remember the ½ for triangles.
Practice
5 questions with new numbers every set. Get 4 of 5 to mark this topic as practiced.