If the perimeter of an equilateral triangle is 60 cm, find its area.

Correct answer: 100√3 cm². Side = 60 ÷ 3 = 20 cm, and area = (√3/4) × 20² = 100√3 cm².

Background: The area of an equilateral triangle is (√3/4) × side².

• √3 cm²: √3 cm² is much too small.
• 60√3 cm²: 60√3 cm² does not match a side of 20 cm.
• 120 cm²: 120 cm² does not match the formula.

Did you know? Perimeter = 3 × side.

Memory trick: Area = (√3/4) a².