WAEC Mathematics 2021 Paper

Concept:In an equilateral triangle, the height $h$ is related to its side $a$ by $h = \frac{\sqrt{3}}{2}a$. The perimeter is the sum of all three equal sides: $P = 3a$.Explanation:Given height of the equilateral triangle: $h = 10\sqrt{3}$ cm.Use the height formula: $10\sqrt{3} = \frac{\sqrt{3}}{2}a$.Multiply both sides by 2: $20\sqrt{3} = a\sqrt{3}$.Divide both sides by $\sqrt{3}$: $a = 20$ cm.Now, perimeter $P = 3a = 3 \times 20 = 60$ cm.Answer:The perimeter of the equilateral triangle is $60$ cm.Therefore, the correct option is B. 60 cm.