Explanation and example

Rectangle: a × b. Triangle: base × perpendicular height / 2. Trapezoid: (a + b) × height / 2, where a and b are parallel bases.

Example: a trapezoid with bases 3 and 5 and height 2 has area (3 + 5) × 2 / 2 = 8 square units.

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Limits

Lengths must be positive and use the same unit. Triangle height must be perpendicular to the chosen base.