Geometry · Quick Reference

Area Cheat Sheet

Geometry · Lesson 10/16

In one line: area measures how much flat space a two-dimensional shape covers — a fundamental measurement with formulas that differ by shape but share the same underlying logic.

Key Ideas

1Area of a Rectangle. Area = length x width.

2Area of a Triangle. Area = (1/2) x base x height.

3Area of a Parallelogram. Area = base x height (the perpendicular height, not the slanted side).

4Area of a Trapezoid. Area = (1/2) x (base1 + base2) x height — the average of the two parallel sides, times the height.

5Area of a Circle. Area = pi x r^2, where r is the radius.

Worked Examples

Find the area of a rectangle with length 8 and width 5.

40 square units

Find the area of a triangle with base 10 and height 6.

30 square units

Find the area of a trapezoid with parallel sides 4 and 8, and height 5.

30 square units

Formulas

Rectangle: A = length * width

Triangle: A = (1/2) * base * height

Parallelogram: A = base * height

Trapezoid: A = (1/2) * (base1+base2) * height

Circle: A = pi * r^2

Practice Yourself

Find the area of a rectangle with length 12 and width 4.

Find the area of a triangle with base 8 and height 5.

Find the area of a parallelogram with base 6 and height 9.